Systems using a levitating, rotating pumping or mixing element and related methods

ABSTRACT

A system for pumping or mixing a fluid using a rotating pumping or mixing element and various other components for use in a pumping or mixing system are disclosed.

This application is: (1) a continuation of Ser. No. 11/496,702, filedJul. 31, 2006, and now U.S. Pat. No. 7,434,983, which is a continuationof Ser. No, 10/398,946, which is the national stage of PCT/US01/31459,filed Oct. 9, 2001, now U.S. Pat. No. 7,086,778, which claims thebenefit of the following U.S. Provisional Patent Applications: (a) Ser.No. 60/239,187, filed Oct. 9, 2000; (b) Ser. No. 60/282,927. filed Apr.10, 2001; and (c) Ser. No. 60/318,579, filed Sep. 11, 2001; and (2) acontinuation-in-part of Ser. No. 10/491,512, now U.S. Pat. No. ______,which is the national stage of PCT/US02/31478, filed Oct. 2, 2002, whichclaims the benefit of U.S. Provisional Patent Application Ser. No.60/326,833, filed Oct. 3, 2001. The disclosures of the foregoingapplications are all incorporated herein by reference.

TECHNICAL FIELD

The present invention relates generally to the mixing arts and, moreparticularly, to a system, related components, and related method forpumping or mixing fluids using a rotatable magnetic element.

BACKGROUND OF THE INVENTION

Most pharmaceutical solutions and suspensions manufactured on anindustrial scale require highly controlled. thorough mixing to achieve asatisfactory yield and ensure a uniform distribution of ingredients inthe final product. Agitator tanks are frequently used to complete themixing process, but a better degree of mixing is normally achieved byusing a mechanical stirrer or impeller (e.g., a set of mixing bladesattached to a metal rod). Typically, the mechanical stirrer or impelleris simply lowered into the fluid through an opening in the top of thevessel and rotated by an external motor to create the desired mixingaction.

One significant limitation or shortcoming of such an arrangement is thedanger of contamination or leakage during mixing. The rod carrying themixing blades or impeller is typically introduced into the vesselthrough a dynamic seal or bearing. This opening provides an opportunityfor bacteria or other contaminants to enter, which of course can lead tothe degradation of the product. A corresponding danger of environmentalcontamination exists in applications involving hazardous or toxicfluids, or suspensions of pathogenic organisms, since dynamic seals orbearings are prone to leakage. Cleanup and sterilization are also madedifficult by the dynamic bearings or seals, since these structurestypically include folds and crevices that are difficult to reach. Sincethese problems are faced by all manufacturers of sterile solutions,pharmaceuticals, or the like, the U.S. Food and Drug Administration(FDA) has consequently promulgated strict processing requirements forsuch fluids, and especially those slated for intravenous use.

In an effort to overcome these problems, others have proposedalternative mixing technologies. Perhaps the most common proposal forstirring a fluid under sterile conditions is to use a rotating,permanent magnet bar covered by an inert layer of TEFLON, glass, or thelike. The magnetic “stirrer” bar is placed on the bottom of the agitatorvessel and rotated by a driving magnet positioned external to thevessel. An example of such an arrangement where the vessel is a flexiblebag is shown in U.S. Pat. No. 5,947,703 to Nojiri et al., the disclosureof which is incorporated herein by reference.

Of course, the use of such an externally driven magnetic bar avoids theneed for a dynamic bearing, seal or other opening in the vessel totransfer the rotational force from the driving magnet to the stirringmagnet. Therefore, a completely enclosed system is provided. This ofcourse prevents leakage and the potential for contamination created byhazardous materials (e.g., cytotoxic agents, solvents with low flashpoints, blood products, etc.), eases clean up, and allows for thedesirable sterile interior environment to be maintained. all of whichare considered significant advantages.

Despite the advantages of this type of mixing systems and others wherethe need for a shaft penetrating into the vessel or dynamic seal iseliminated, a substantial, but heretofore unsolved problem with suchsystems is the difficulty in coupling a fluid-agitating element with anexternal motive device providing the rotation and/or levitation force.For example, when a vessel in the form of a flexible bag containing anunconfined fluid-agitating element is positioned in proximity to themotive device, the relative location of the fluid-agitating element isgenerally unknown. In the case of a small (10 liter or less) transparentbag, it is possible to manipulate the bag relative to the motive devicein an effort to ensure that the fluid-agitating, element is “picked up”and the desired coupling, is formed. However, this is consideredinconvenient and time consuming, especially if fluid is already presentin the bag. Moreover, in the case where the bag is relatively large(e.g., capable of holding 100 liters or more) or formed of an opaquematerial (e.g., black), achieving the proper positioning of thefluid-agitating element relative to the external motive device is at aminimum difficult, and in many cases, impossible. In the absence offortuity, a significant amount of time and effort is required to liftand blindly reposition the bag relative to the motive device, withoutever truly knowing that the coupling is properly formed. Also, even ifthe coupling is initially formed, the fluid-agitating element may becomeaccidentally decoupled or disconnected from the motive device during themixing operation. In view of the semi-chaotic nature of such an event,the ultimate resting place of the fluid-agitating element is unknownand, in cases where the fluid is opaque (e.g. blood) or cloudy (e.g.cell suspensions), not easily determined. If the coupling ultimatelycannot be established in the proper fashion, the desired fluid agitationcannot be achieved in a satisfactory manner, which essentially rendersthe set up useless. These shortcomings may significantly detract fromthe attractiveness of such fluid agitation systems from a practicalstandpoint.

In many past mixing arrangements, a rigid vessel is used with afluid-agitating element directly supported by a post carrying a rollerbearing, with the rotational force being supplied by an external device(see, e.g., U.S. Pat. No. 4,209,259 to Rains et al., the disclosure ofwhich is incorporated herein by reference). While this direct supportarrangement prevents the fluid-agitating, element from being lost in theevent of an accidental decoupling, the use of such post or likestructure in a bag for receiving and holding a fluid-agitating elementhas not been proposed. The primary reason for this is that, in a typicalflexible bag, neither the sidewalls nor any other structure is capableof providing the direct support for the fluid-agitating element or acorresponding bearing.

Thus, a need is identified for an improved manner of ensuring that thedesired coupling may be reliably achieved between a fluid-agitatingelement in a vessel such as a bag and an external motive device. such asone supplying the rotational force that causes the element to agitatethe fluid, even in large, industrial scale mixing bags or vessels(greater than 100 liters), opaque bags or vessels, or where the fluid tobe agitated is not sufficiently clear, and even after an accidentaldecoupling occurs. The improvement provided by the invention would beeasy to implement using existing manufacturing techniques and withoutsignificant additional expense. Overall, a substantial gain inefficiency and ease of use would be realized as a result of theimprovement, and would greatly expand the potential applications forwhich advanced mixing systems may be used.

SUMMARY OF THE INVENTION

One aspect of the disclosure is an apparatus for mixing a fluid. Theapparatus comprises a vessel including a flexible wall at leastpartially defining an interior compartment capable of receiving andholding the fluid. The apparatus further comprises a fluid-agitatingelement in the interior compartment of the vessel. and a receiversecured to the flexible wall of the vessel for receiving thefluid-agitating element.

In one embodiment, the fluid-agitating element is disengaged from thereceiver and capable of rotating relative to the receiver and movingtoward or away from the wall of the vessel. Preferably, the receiverincludes a retainer for retaining the fluid-agitating element, which mayinclude a passage for receiving the receiver. The passage has an openingat one end with a transverse dimension larger than a correspondingdimension of the receiver.

Preferably, the receiver comprises an imperforate sidewall forming acavity. The receiver may further include an inner surface for contactingthe fluid when present in the vessel and an outer surface external tothe interior compartment for positioning adjacent a motive device forrotating the fluid-agitating element (which may have an upper portionmatching the outer surface as well). Still more preferably thefluid-agitating element includes a home or resting position and iscapable of levitating relative to the receiver to an active position.The fluid-agitating element may comprise a substantially cylindricalbody having an outer wall spaced from a sidewall of the receiver. Mostpreferably, the flexible wall of the vessel includes an opening, and thereceiver is at least partially within the opening of the vessel.

Another aspect of the disclosure is an apparatus for mixing a fluidcomprising a vessel including a flexible wall at least partiallydefining an interior compartment capable of receiving and holding thefluid. The apparatus further comprises a rotatable fluid-agitatingelement for agitating the fluid in the interior compartment of thevessel. The vessel further includes a receiver having a projectingportion with a sidewall and an end wall defining a cavity, saidprojecting portion including an outer surface in communication with theenvironment exterior to the interior compartment of the vessel and aninner surface within the interior compartment of the vessel and adjacentthe fluid-agitating element.

Preferably, the fluid-agitating element is positioned adjacent the innersurface of the cavity within the vessel and retained adjacent thereceiver by a coupling. A retainer may also be included for providing aretention function to maintain the fluid-agitating element adjacent theinner surface of the cavity. A rotatable rod may be positioned in thecavity adjacent the outer surface, with the rod adapted for beingrotated by a motor for inducing rotation in the fluid-agitating element.To facilitate rotation of the rod relative to the vessel, a bearing maybe provided. Most preferably, the bearing is positioned between a motorfor rotating the rod and the vessel.

In accordance with yet another aspect of the disclosure, an apparatusfor mixing a fluid is provided. The apparatus comprises an at leastpartially flexible vessel including an interior compartment, means foragitating the fluid when present in the interior compartment, and meansfor receiving the fluid-agitating element. In one, exemplary embodiment,the means for agitating comprises a rotatable fluid-agitating elementfor positioning in the interior compartment of the vessel in contactwith the fluid when present. In this or another embodiment, the meansfor receiving the fluid-agitating element comprises a post. Thereceiving means may comprise a projecting portion of the vessel, saidprojecting portion having a sidewall and an end wall defining a cavity,with the projecting portion further including an outer surface incommunication with the environment exterior.[

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings incorporated in and forming a part of thespecification illustrate several aspects of the present invention and,together with the description, assist in explaining the principles ofthe invention. In the drawings:

FIG. 1 is a partially cross-sectional, partially cutaway, partiallyschematic view of one embodiment of the system of the present inventionwherein the levitating pumping or mixing element is rotated by anexternal drive or driving magnet to mix a fluid in a vessel and thecooling source is a separate cooling chamber defined by the outer wallof a cryostat holding a cryogen;

FIG. 2 is an enlarged cross-sectional, partially cutaway, partiallyschematic view of an embodiment wherein the rotating, levitating pumpingor mixing element is used to pump a fluid through a vessel positionedadjacent to the housing for the superconducting element and the coolingsource is a closed cycle refrigerator;

FIG. 3 is a partially cross-sectional, partially cutaway, partiallyschematic view of the system of the first embodiment wherein thesuperconducting element, vessel, pumping or mixing element, and drivemagnet are axially aligned, but moved off-center relative to thevertical center axis of the vessel;

FIG. 4 a is a bottom view of the drive magnet used in situations whereexceptional rotational stability of the pumping or mixing element of thepreferred embodiment is required;

FIG. 4 b is a partially cross-sectional, partially cutaway side view ofthe system showing the drive magnet of FIG. 4 a magnetically coupled toa similarly constructed second permanent magnet forming a pail of thepumping or mixing element;

FIG. 4 c is one possible embodiment of the pumping or mixing systemincluding a pumping or mixing element having a chamber for holding asubstance that is lighter than the surrounding fluid, such as air, thatassists in levitating the pumping or mixing element;

FIG. 5 is a partially cross-sectional, partially schematic side view ofa second possible embodiment of a pumping or mixing system using apumping or mixing element levitated by a thermally isolated coldsuperconducting element wherein the motive force for rotating thepumping or mixing element in the vessel is provided by rotating thesuperconducting element itself;

FIG. 6 a is a top schematic view of one possible arrangement of thelevitating pumping or mixing element that may be driven by a rotatingsuperconducting element;

FIG. 6 b shows the pumping or mixing element of FIG. 6 a levitatingabove a rotating superconducting element formed of two component parts;

FIG. 7 is a partially cutaway, partially cross-sectional schematic sideview of a vessel in the form of a centrifugal pumping head. including alevitating, rotating pumping or mixing element for pumping fluid fromthe inlet to the outlet of the centrifugal pumping head;

FIG. 8 a shows an alternate embodiment of a pumping or mixing elementespecially adapted for levitation in a vessel or container having arelatively narrow opening;

FIG. 5 b shows another alternate embodiment of a pumping or mixingelement adapted especially for use in a vessel or container having arelatively narrow opening;

FIG. 5 c illustrates the pumping or mixing element of FIG. 8 b in apartially folded state for insertion in the narrow opening of a vesselor container;

FIG. 9 is a partially cross-sectional, partially schematic side view ofa second embodiment of a pumping or mixing system wherein separatelevitating and driven magnets are carried on the same, low-profilepumping or mixing element, with the levitation being supplied by athermally isolated superconducting element and the rotary motion beingsupplied a motive device including driving magnets coupled to a rotatingshaft and positioned in an opening in the evacuated or insulated chambersurrounding the superconducting element;

FIG. 9 a is a top or bottom view of one possible embodiment of a pumpingor mixing element for use in the system of FIG. 9;

FIG. 9 b is a partially cross-sectional side view of the pumping ormixing element of FIGS. 9 and 9 a levitating above the superconductingelement, and illustrating the manner in which the driven magnets arecoupled to the corresponding driving magnets to create the desiredrotational motion;

FIG. 10 is a top view of a most preferred version of a cryostat for usewith the pumping and mixing system of the embodiment of FIG. 9;

FIG. 11 is a partially cutaway, partially cross-sectional side schematicview of a centrifugal pumping head for use with the system of FIG. 9;

FIG. 12 is a cross-sectional side view of another possible embodiment ofa pumping or mixing system of the present invention;

FIG. 12 a is a cross-sectional view taken along line 12 a-12 a of FIG.12;

FIG. 12 b is a cross-sectional view taken along line 12 b-12 b of FIG.12;

FIG. 12 c is a cross-sectional view of the embodiment of FIG. 12, butwherein the motive device is in the form of a winding around the vesselfor receiving an electrical current that creates an electrical field andcauses the pumping or mixing element to rotate;

FIG. 13 is an alternate embodiment of an inline levitating pumping ormixing element, similar in some respects to the embodiment of FIG. 9;

FIG. 14 is an enlarged partially cross-sectional, partially cutaway sideview showing the manner in which a sealed flexible bag carrying apumping or mixing element may be used for mixing a fluid, and alsoshowing one example of how a transmitter and receiver may be used toensure that the proper pumping or mixing element is used with thesystem;

FIG. 14 a is an enlarged, partially cross-sectional, partially cutawayside view showing an attachment including a coupler for coupling withthe pumping or mixing element;

FIG. 14 b is an enlarged, partially cross-sectional, partially cutawayside view showing a mixing vessel having centering and alignmentstructures;

FIG. 14 c is an enlarged, partially cross-sectional, partially cutawayside view slowing an alternate orientation of the vessel with centeringand alignment structures;

FIG. 14 d is an enlarged, partially cross-sectional, partially cutawayside view showing the use of a second motive device in the system ofFIG. 14, such as a linear motion device, for moving the super-conductingelement, and hence, the pumping or mixing element to and fro inside ofthe vessel;

FIG. 14 e is an enlarged, partially cross-sectional, partially cutawayside view showing a mixing vessel having centering arid alignmentstructures;

FIG. 15 illustrates one charging magnet including a spacer that may formpart of a kit for use in charging the superconducting element as it iscooled to the transition temperature, as well as a heater for warningthe superconducting element to above the transition temperature forrecharging;

FIG. 16 is as partially cross-sectional, mainly schematic view of allembodiment of the system for use with a vessel having a thin-wailedcavity;

FIG. 16 a is a partially cutaway, partially cross-sectional top view ofthe cryostat of FIG. 16;

FIG. 17 is an enlarged, schematic view showing, a superconductor orsuperconducting element comprised of a plurality of segments of asuperconducting material having crystallographic planes for levitating aconcentric annular levitation magnet, and slowing in particular adesired orientation of the crystallographic C-axis of each segmentrelative to the magnetization vector of the levitation magnet;

FIG. 18 is a cross-sectional view taken along line 18-18 of FIG. 17;

FIG. 19 is an embodiment wherein a plurality of superconductors orsuperconducting elements are used to levitate a pumping or mixingelement in a fluid containing vessel, and again showing in particular adesired orientation of the crystallographic C-axis of each segmentrelative to the magnetization vector of the levitation magnet;

FIG. 19 a is a top view of the cryostat and a portion of the motivedevice in the system of FIG. 19;

FIG. 20 illustrates an embodiment where the cryostat includes acryocooler which rotates along with the superconducting element to bothlevitate and rotate the pumping or mixing element in a vessel, which isshown as having a cavity formed therein;

FIG. 21 is a schematic view showing one possible orientation of themagnets and superconductors in the embodiment of FIG. 20;

FIG. 22 illustrates a flexible bag or container having a cavity formedtherein, which in addition to receiving the head end of the cryostat mayalso act as a centering post for a concentric pumping or mixing element;and

FIG. 23 illustrates an embodiment where permanent magnets are used toprovide a levitation-assist function to prevent the pumping or mixingelement from contacting the adjacent vessel;

FIG. 24 is another embodiment where permanent magnets are used toprovide a levitation-assist function to prevent the pumping or mixingelement from contacting the adjacent vessel;

FIG. 25 is yet another embodiment where permanent magnets are used toprovide a levitation-assist function to prevent the pumping or mixingelement from contacting the adjacent vessel;

FIG. 26 is a partially cross-sectional view showing a vessel includingan engagement structure for engaging and supporting the pumping ormixing element when in a non-levitating condition; and

FIG. 27 is a partially cross-sectional view showing the moving of thecryostat to in turn move the magnetically coupled pumping or mixingelement of FIG. 26 to a levitated position.

DETAILED DESCRIPTION OF THE INVENTION

Reference is now made to FIG. 1, which shows a first possible embodimentof the mixing or pumping system 10 of the present invention. In thisembodiment, a cryostat 12 is used to hold the cooling source for thesuperconducting element that produces the desired levitation in apumping or mixing element 14. This element 14 is placed in a vessel 16positioned external to the cryostat 12. The vessel 16 may alreadycontain a fluid F or may be filled after the pumping or mixing element14 is in place. It should be appreciated at the outset that the term“fluid” is used herein to denote any substance that is capable offlowing, as may include fluid suspensions, gases, gaseous suspensions,or the like, without limitation. The vessel 16 for holding the fluid isshown as being cylindrical in shape and may have an open top.Alternatively, it may be completely sealed from the ambient environmentto avoid the potential for fluid contamination or leakage during mixing,or adapted to pump the fluid F from an inlet to an outlet in the vessel16 (see FIG. 2). In any case, the vessel 16 may be fabricated of anymaterial suitable for containing fluids, including glass, plastic,metal, or the like. Of course, the use of lightweight plastic or otherhigh density polymers is particularly desirable if the vessel 16 isgoing to be discarded after mixing or pumping is complete, as set forthin more detail in the description that follows.

As illustrated in FIG. 1, the vessel 16 rests atop the outer wall 18 ofthe cryostat 12. Preferably, this outer wall 18 is fabricated ofnon-magnetic stainless steel, but the use of other materials is ofcourse possible, as long as the ability of the pumping or mixing element14 to levitate and rotate remains substantially unaffected. Positionedinside of and juxtaposed to this wall 18 is a superconducting element20. The superconducting element 20 is supported by a rod 22 that servesas the thermal link to a cooling source 24. The outer wall 18 of thecryostat 12 thus defines a chamber 25 that is preferably evacuated tothermally isolate the cold superconducting element 20 from therelatively warm vessel 16, pumping or mixing element 14, and fluid F.Positioning of the superconducting element 20 in this vacuum chamber 25may be possible by virtue of the thermal link provided by the rod 22.The thermal isolation and separation provided by the chamber 25 allowsfor the superconducting element 20 to be placed in very close proximityto the outer wall 18 without affecting its temperature, or thetemperature of the vessel 16. This allows the separation distance fromthe superconducting element 20 to the inner surface of the wall 18 to benarrowed significantly, such that in the preferred embodiment, the gap Gbetween the two is preferably under 10 millimeters, and can be as narrowas approximately 0.01 millimeters. This substantial reduction in theseparation distance enhances the levitational stability, magneticstiffness. and loading capacity of the pumping or mixing element 14.

In this first illustrated embodiment, the cooling source 24 is aseparate, substantially contained cooling chamber 26 holding a cryogenC, such as liquid nitrogen. The chamber 26 is defined by an outer wall28 that is substantially thermally separated from the outer wall 18 ofthe cryostat 12 to minimize heat transfer. An inlet I is providedthrough this wall 28 for introducing the cryogen into the coolingchamber 26. To permit any vapor P to escape from the chamber 26 as thecryogen C warms, an exhaust outlet O is also provided (see action arrowsin FIG. 1 also designating the inlet and outlet). In the illustratedembodiment, the inlet I and outlet O lines may formed of a materialhaving a low thermal conductivity, such as an elongate, thin walled tubeformed of nonmagnetic stainless steel, and are sealed or welded in placeto suspend the cooling chamber 26 in the cryostat 12. As should beappreciated by one of ordinary skill in the art, the use of a thinwalled tube formed of a material having a low thermal conductivity, suchas stainless steel, results in a negligible amount of thermal transferfrom the inlet or outlet to the wall 18. The sealing or welding methodemployed should allow for the chamber 25 to be maintained in anevacuated state, if desired. Despite this illustration of one possiblesupport arrangement, it should be appreciated that the use of any othersupport arrangement that minimizes thermal transfer between the coolingchamber 26 and the cryostat wall or other housing 18 is also possible(see, e.g., my '672 patent).

The rod 22 serving as the thermal link between the cooling source 24 andthe superconducting element 20 may be cylindrical and may extend throughthe outer wall 28 of the cooling chamber 26. The entire surface area ofthe superconducting element 20 should contact the upper surface of thecylindrical rod 22 to ensure that thermal transfer is maximized. The rod22 may be formed of materials having low thermal resistance/high thermalconductance, such as brass, copper, or aluminum.

As should be appreciated from viewing FIG. 1, and as briefly noted inthe foregoing description, the combination of the outer wall 18 and theinner cooling chamber 26 in this first embodiment defines the chamber 25around the superconducting element 20. Preferably, this chamber 25 isevacuated to minimize heat transfer from the cooling chamber walls 28and the superconducting element 20 to the outer wall 18 of the cryostat12. The evacuation pressure is preferably at least 10⁻³ torr, and mostpreferably on the order of 10⁻⁵ torr but of course may vary dependingupon the requirements of a particular application. The important factoris that thermal transfer from the cooling source 24, which in this caseis the cooling chamber 26 holding a cryogen C, and the superconductingelement 20 to the outer wall 18 is minimized to avoid cooling the vessel16 or fluid F held therein. Although a vacuum chamber 25 is proposed asone preferred manner of minimizing this thermal transfer, the use ofother means to provide the desired thermal isolation is possible, suchas by placing insulating materials or the like in the chamber 25.

As is known in the art, by cooling the super-conducting element 20 inthe presence of a magnetic field, it becomes capable of distributing thecurrent induced by a permanent magnet such that the magnet levitates acertain distance above the superconducting element, depending primarilyupon the intensity and the direction of the magnetic field generated bythe levitating magnet. Although basically a repulsive force is created,the peculiar nature of the pinning forces generated actually tie thelevitating magnet to the superconducting element as if the two wereconnected by an invisible spring. As should be appreciated, this form ofattachment cannot be achieved in conventional levitation schemes forpumping or mixing elements that employ two opposed permanent magnetsthat merely repel each other, since no pinning forces act to tie the twomagnets together, while at the same time provide a balancing repulsiveforce.

In the preferred embodiment of the present system 10, the element 20providing the superconductive effects is a “high temperature” or “typeII” superconductor. Most preferably, the superconducting element 20 isformed of a relatively thin cylindrical pellet of melt-texturedYttrium-Barium Copper Oxide (YBCO) that, upon being cooled to atemperature of approximately 77-78 Kelvin using a cooling source 24,such as the illustrated liquid nitrogen chamber 26, exhibits the desiredlevitational properties in a permanent magnet. Of course, the use ofother known superconducting materials having higher or lower operatingtemperatures is also possible, and my prior U.S. Pat. No. 5,567,672 isincorporated herein by reference for, among, other things, the otherhigh-temperature superconducting materials referenced therein.

The pumping or mixing element 14 in the preferred embodiment includes afirst permanent magnet 32 for positioning in the vessel 16 adjacent tothe superconducting element 20 such that it levitates in the fluid F.Although the polarity of this first magnet 32 is not critical tocreating the desired levitation, the magnet 32 is preferably disk-shapedand polarized in the vertical direction. This ensures that a symmetricalmagnetic field is created by the magnet 32 and stable levitation resultsabove the superconducting element 20, while at the same time freerotation relative to the vertical axis is possible.

In a version of the pumping or mixing element 14 particularly adaptedfor use in relatively deep fluid vessels, a support shaft 34 isconnected to and extends vertically from the first permanent magnet 32.Along the shaft 34, at least one, and preferably two, impellers 36 arecarried that serve to provide the desired pumping, or in the case ofFIG. 1, mixing action when the pumping or mixing element 14 is rotated.Rotation of the levitating pumping or mixing element 14 in the vessel 16is achieved by a magnetic coupling formed between a second permanentmagnet 38 (shown in dashed line outline in FIG. 1, but see also FIG. 2)and a drive magnet 40 positioned externally of the vessel 16. The drivemagnet 40 is rotated by a drive means, such as an electric motor 42 orthe like, and the magnetic coupling formed with the second permanentmagnet 38 serves to transmit the driving torque to the pumping or mixingelement 14 to provide the desired pumping or mixing action. Thedirection of rotation is indicated by the action arrows shown in FIGS. 1and 2 as being in the counterclockwise direction, but it should beappreciated that this direction is easily reversed by simply reversingthe direction in which the drive magnet 40 is rotated.

In operation, and in practicing one possible method of pumping or mixinga fluid disclosed herein, the vessel 16 containing the fluid F andpumping or mixing element 14 are together placed external to the wall 18of the cryostat 12 adjacent to the superconducting element 20, which isplaced in the evacuated or insulated chamber 25. When the firstdisk-shaped permanent magnet 32 is brought into the proximity of thesuperconducting element 20, the symmetrical magnetic field generatedcauses the entire pumping or mixing element 14 to levitate in a stablefashion above the bottom wall of the vessel 16. This levitation bringsthe second permanent magnet 38 into engagement with the drive magnet 40to form the desired magnetic coupling. In addition to transmitting thedriving torque, this magnetic coupling also serves to stabilize rotationof the pumping or mixing element 14. The motor 42 or other motive deviceis then activated to cause the drive magnet 40 to rotate, which in turninduces a steady, stable rotation in the pumping or mixing element 14.Rotating impellers 36 then serve to mix or pump the fluid F in a gentle,yet thorough fashion.

Since the pumping or mixing element 14 fully levitates and can becompletely submerged in the fluid, the need for mixing or stirring rodspenetrating through the vessel 16 in any fashion is eliminated. Theconcomitant need for dynamic shaft seals or support hearings in thevessel walls is also eliminated. Deleterious friction is also not aconcern. A related advantage is that the vessel 16 containing the fluidF and the pumping or mixing element 14 call be completely sealed fromthe outside environment before mixing to provide further assurancesagainst leakage or contamination. Yet another related advantagediscussed in detail below is that the vessel 16 and pumping or mixingelement 14 can be formed of relatively inexpensive, disposable materialsand simply discarded once mixing is complete. As should be appreciated,this advantageously eliminates the need for cleanup and sterilization ofthe pumping or mixing element 14 and vessel 16. Thus, by completelysealing a disposable vessel. such as a plastic container or flexible bagcontaining the pumping or mixing element and fluid prior to mixing, theentire assembly can simply be discarded once the fluid contents arerecovered. This reduces the risk of exposure both during and aftermixing in the case of hazardous fluids, and also serves to protect thefluid from contamination prior to or during the pumping or mixingoperation.

An alternative version of this first possible embodiment of the system10 of the present invention particularly adapted for pumping a fluid Fis shown in FIG. 2. In this version, the vessel 16 includes at least onefluid inlet 44 and at least one outlet 46. The pumping or mixing element14 preferably carries rotating impellers 36 that serve to provide thedesired pumping action by forcing fluid F from the inlet 44 to theoutlet 46 (see action arrows). By increasing or decreasing therotational speed of the motor 42 or other motive device, or adjustingthe size, shape or style of the pumping or mixing element 14, impeller.blades 36, or substituting a different design altogether, a preciselevel of pumping action may be provided.

Another possible modification shown in FIG. 2 is to use a closed cyclerefrigerator 48 to provide the necessary cooling for the superconductingelement 20 instead of a cryostat with a liquid cryogen as the coolingsource. The refrigerator 48 can be positioned externally to a housing 18containing the superconducting element 20, which may be the equivalentof the cryostat outer wall 18 previously described. As with the firstembodiment, a chamber 25 is defined by the housing 18. This chamber 25is preferably evacuated or filled with other insulating materials tominimize thermal transfer from the superconducting element 20 to thehousing 18. However, since no cooling source 24 is contained within thehousing 18, it is not actually a “cryostat” as that term is commonlydefined. Nevertheless, the desired dual levels of thermal separation arestill possible, and the concomitant advantages provided, since: (1) thecooling source 24, 48 is positioned away from the housing 18 and, thus,the vessel 16, pumping or mixing element 14, and fluid F; and (2) thehousing 18 still separates and defines a chamber 25 that thermallyisolates the superconducting element 20 and the vessel 16. In yetanother alternate arrangement, the refrigerator 48 can be used as aprimary cooling source. with the cryogenic chamber (not shown) servingas a secondary or “backup” cooling source in the event of a power outageor mechanical failure.

In accordance with another of the many important aspects of the presentsystem 10, the absence of a mixing rod or other mechanical stirrerextending through a wall of the vessel 16 also allows for placement ofthe pumping or mixing element 14 at an off-axis position, as shown inFIG. 3. Specifically, the superconducting element 20, pumping or mixingelement 14, and drive magnet 40 are all axially aligned away from thevertical center axis of the vessel 16. One particular advantage of usingthis approach is that the pumping or mixing element 14 may be rotated ata very low speed while the vessel 16 is also rotated about its centeraxis. This advantageously ensures that gentle, yet thorough mixing, isachieved, which is particularly advantageous for use with fluids thatare sensitive to shear stress. As should be appreciated, thisarrangement can be used both whether the vessel 16 is completely sealed,provided with an inlet 44 and an outlet 46 for pumping as shown in FIG.2, or open to the ambient environment. For purposes of illustrationonly, FIG. 3 shows the cryostat 12 of the embodiment shown in FIG. 1having an outer wall 18 and a cooling chamber 26 defined by a wall 28.However. it should be appreciated that use of the housing 18 andclosed-cycle refrigerator 48 of the second embodiment of FIG. 2 as partof the “cryostat” is also possible with this arrangement.

Through experimentation, it has been discovered that when the pumping ormixing element 14 of the type described for use in this first possibleembodiment is employed, providing the requisite degree of stability toensure that all contact with the side walls of the container 16 isavoided may in some instances be a concern. Thus, to ensure that thepumping or mixing element 14 rotates with exceptional stability and suchdeleterious contact is completely avoided, the second permanent magnet38 and the drive magnet 40 are each provided with at least two pairs,and preferably four pairs of cooperating sub-magnets 50 a, 50 b. Asshown in FIGS. 4 a and 4 b, these magnets 50 a, 50 b have oppositepolarities and thereby serve to attract each other and prevent thelevitating pumping or mixing element 14 from moving from side-to-side toany substantial degree. However, the attractive force is counterbalancedby the combined spying-like attractive and repulsivelevitational/pinning forces created between the first permanent magnet32 and the superconducting element 20 when cooled. This avoids thepotential for contact with the upper wall of the vessel 16, if present.Overall, the pumping or mixing element 14 is capable of exceptionallystable rotation using this arrangement, which further guards against theundesirable frictional beating or shear stress created if the rotatingpumping or mixing element 14, or more particularly, the first and secondpermanent magnets 32, 38 or the blades of the impellers 36 could moveinto close proximity with the bottom or side walls of the vessel 16.

As should be appreciated, it is possible to rearrange the components ofthe system 10 such that the levitation and driving forces are providedfrom other areas of the vessel, rather than from the top and bottom ofthe vessel. Thus, as shown in FIG. 4 c, the cryostat 12 or other housingtoy containing the super-conducting element 20 may be positionedadjacent to one side of the vessel 16, while the drive magnet 40 ispositioned adjacent to the opposite side. In that case, the pumping ormixing element 14 may be turned on its side and supported by a separatestable support structure, such as a table T or the like. The vessel 14is shown as being sealed, but it should be appreciated that any of thevessels disclosed herein may be employed instead, including even astraight or L-shaped pipe.

To assist in levitating the pumping or mixing element 14 in either theembodiment of FIG. 1 or 2 or the other embodiments disclosed herein, atleast one, and preferably a plurality of chambers 60 are provided forcontaining a substance lighter than the surrounding fluid F. Thechambers 60 may be provided adjacent to each magnet 32, 38 in thepumping or mixing element 14, as well as around the shaft 34, ifdesired. In the preferred embodiment where the fluid F is or has aspecific gravity similar to that of water, the substance contained inthe chambers 60 may be air. However., in more viscous fluids, such asthose having a specific gravity more like glycerin, it may be possibleto use lighter fluids, such as water, even lighter gases, orcombinations thereof. These chambers 60 thus serve to assist inlevitating the pumping or mixing element 14 by helping it “float” in thefluid F. However, the “pinning” force created by the superconductingelement 20. plus the levitating and aligning force created between thesecond permanent magnet 38 and the driving magnet 40, both also serve toassist in keeping the pumping or mixing element 14 in the properposition as it rotates. In the case of disk or pancake shaped permanentfirst and second magnets 32, 38 and a cylindrical shaft 34, annularchambers 60 may be used. Instead of fluid or gas filled chambers, theuse of other buoyant materials is also possible to provide thelevitation-assist function.

As previously mentioned, one of the many advantages of the system 10 ofthe present invention is that, since the pumping or mixing element 14levitates in the fluid F and no mixing or stirring rods are required forrotation, the vessel 16 can be completely sealed from the outsideambient environment. Thus, by forming the pumping or mixing element 14and vessel 16 of relatively inexpensive or disposable materials, bothcan simply be discarded after mixing is completed and the fluid F isrecovered. Of course, such disposable materials can also be used to formthe vessel 16 designed for pumping fluids (FIG. 2), or to form theopen-top container for mixing fluids to avoid the need for clean up orsterilization once the operation is complete.

It should also be appreciated that the pumping or mixing element 14illustrated is an example of one preferred arrangement only, and thatother possible configurations are possible. For instance, impellerblades are not required, since a smooth-walled, disk-shaped pumping ormixing element alone creates some gentle mixing action simply byrotating. If present, the blade or blades could simply be placedcircumferentially around the disk-shaped first permanent magnet 32 toreduce the length of the shaft 34, or eliminate it altogether,especially if the vessel 16 has a relatively small vertical dimension.Instead of a bladed impeller assembly 36, the use of other structuralarrangements is also possible, such as disk-shaped wheels having vanesor like structures designed to create more or less efficient rotation,and a concomitant increase in the desired mixing or pumping action whenrotated. Depending on the depth of the vessel 16, the length of theshaft 34, if present, can also be increased or decreased as necessary.All components forming the pumping or mixing element in any embodimentdescribed above may be coated with TEFLON or other inert materials toreduce the chances of contamination or corrosion, as well as tofacilitate clean up, if required.

Of course, besides use in the mixing or pumping of small batches offluid solutions or suspensions used during experimentation and researchin the laboratory setting, all components are also easily scaled up foruse in industrial or commercial pumping or mixing operation, such asthose commonly used in the manufacture of large batches pharmaceuticalsor food products. The stable, reliable levitation of the magneticpumping or mixing element can still be readily achieved in systems ofmuch greater capacity than the one shown for purposes of illustration inthe drawings, thus making the present arrangement particularlywell-suited for the commercial production of pharmaceuticals or anyother solutions or suspensions that require gentle, yet thorough mixingduring processing.

Experiments conducted to date have demonstrated the efficacy of thesystem 10 described above. The set-up utilized in conducting theseexperiments included a pumping or mixing element having axially alignedupper and lower magnets and an impeller assembly mounted on a verticallyextending support shaft, as shown in FIG. 1. A cylindrical pellet ofmelt-textured YBa₂Cu₃O_(7+x) having a diameter of 30 millimeters and athickness of 25 millimeters was used as the superconducting element andplaced in a cryostat having a configuration similar to the one shown inFIG. 1. The cryostat included a cooling chamber filled withapproximately 1 liter of liquid nitrogen. A Nd—Fe—B permanent magnetwith a surface field intensity of 0.4 Tesla was used as the lower, firstpermanent magnet.

Using this set-up, the experiments demonstrated that the desiredexceptionally stable levitation of the pumping or mixing element abovethe top surface of the cryostat in a vessel filled with a relativelywarm fluid was possible. A separation distance of up to sevenmillimeters was achieved, and the levitation was stable for up to fivehours using just a liter of liquid nitrogen as the cryogen. In the firstexperiment using this set up, water was selected as a model lowviscosity fluid. Rotational speeds of up to 600 rpm were achieved thisupper limit being defined by only the limited capabilities of the motorused to rotate the drive magnet in this experiment. No decouplinginstability in the pumping or mixing element was observed at any speed.In the case of glycerin, a model high viscosity fluid, a maximumrotational speed of 60 rpm was achieved before some decoupling of thepumping or mixing element was observed. To further demonstrate themixing capabilities using the proposed system, SEPHADEX powder (drybead, 50-150 micron diameter) was placed on the bottom of a water-filledvessel and the levitating pumping or mixing element rotated. A uniformsuspension was achieved after approximately five minutes of mixing.

As should be appreciated, the system 10 described above and shown inFIGS. 1-4 is based on the use of a stationary superconducting element 20and a pumping or mixing element 14 that, in addition to a “levitation”magnet, includes one or more separate driven magnets for coupling with adrive mechanism, such as one positioned at the opposite end of thevessel or container relative to the superconducting element. However,other embodiments of the pumping or mixing system may include alevitating, rotating pumping or mixing element with magnets that aresimultaneously used not only for levitation, but also for transmittingdriving torque. In one embodiment, this driving torque is simultaneouslyprovided by the pinning forces that couple the pumping or mixing elementwith a rotating superconducting element. Thus, the superconductingelement causes the pumping or mixing element to both levitate androtate, even though there is no physical contact between the twoelements.

More specifically, and in accordance with this second possibleembodiment of the present invention illustrated in FIG. 5, the limitedor mixing system 100 includes a cryostat 102, which may be formed of twoseparate components: a first component 102 a including an outer wall 104that surrounds a relatively thin, disk-shaped superconducting element106 to define a chamber 108, and a second component 102 b including thecooling source 110. Preferably. the outer wall 104 is formed of thin,nonmagnetic material, such as non-magnetic stainless steel or the like,but the use of other materials is possible, as long as they do notinterfere with the operation of the system 100 and have relatively poorthermal conductivity. The chamber 108 surrounding the superconductingelement 106 may be evacuated or insulated as described above tothermally isolate and separate it from the wall 104. However, in thisembodiment, and as noted further below, it is possible to eliminate thechamber 108 entirely in the case where a non-temperature sensitive fluidis being pumped or mixed.

In the case where the chamber 108 is evacuated, a valve 112 may beprovided in the outer wall 104 for coupling to a vacuum source. Anoptional getter 114 (such as an activated carbon insert or the like) maybe positioned in the chamber 108 for absorbing any residual gases andensuring that the desired evacuation pressure is maintained. As with theembodiments described above. the evacuation pressure is preferably onthe order of 10⁻³ torr or greater, but may vary depending on theparticular application.

The superconducting element 106 is supported in the chamber 108independent of the outer wall 104 of the first portion 102 a of thecryostat 102. The support may be provided by a platform 116 that isenclosed by wall 104 and supported at one end of an elongated thermallink 118, preferably formed of metal or another material having a highdegree of thermal conductivity (e.g., 50 Watts/Kelvin or higher). Tosupply the necessary cooling to the superconducting element, theopposite end of the elongated thermal link 118 is positioned in contactwith the cooling source 110, which as described above forms a part ofthe second component 102 b of the “cryostat” 102 (the term cryostatbeing used throughout to denote a structure or combination of structuresthat are capable of maintaining a superconducting element in a coldstate, whether forming a single unit or not). The cooling source 110 isillustrated schematically as an open-top container 119, such as a Dewarflask, containing a liquid cryogen C, such as nitrogen. However, it isalso possible to use a closed-cycle refrigerator or any other devicecapable of supplying the cooling necessary to levitate a magnet above asuperconducting element after field cooling is complete. In the casewhere the wall 104 of the first portion 102 a of the cryostat 102 makescontact with the cryogenic fluid C. as illustrated, it should beappreciated that there is only negligible thermal transfer to theportion of the wall 104 adjacent the vessel, since: (1) the wall 104 maybe formed of a thin material having low thermal conductivity; and (2)the portion of the wall 104 adjacent to the vessel is surrounded by theambient, room-temperature environment.

To permit the superconducting element 106 to rotate, a roller hearingassembly 120 comprising one or more annular roller bearings 122 supportsthe first portion of the cryostat 102 a, including the wall 104 definingthe chamber 108. As should be appreciated from viewing FIG. 5, theseroller bearings 122 permit the first portion of the cryostat 102 ahousing the superconducting element 102 to rotate about an axis, whichis defined as the axis of rotation. A bearing housing 124 or the likestructure for supporting the bearing(s) 122 is secured to an adjacentstable support structure 126. In the illustrated embodiment, a motivedevice includes an endless belt 128 that serves to transmit rotationalmotion from the pulley 129 keyed or attached to the shaft 130 of a motor131 to the first portion of the cryostat 102 a. The motor 131 may be avariable speed, reversible electric motor, but the use of other types ofmotors to create the rotary notion necessary to cause thesuperconducting element 106, and more particularly, the first portion ofthe cryostat 102 a housing the superconducting element 106, to rotate ispossible.

The vessel 132 containing the fluid to be mixed (which as describedbelow can also be in the form of a centrifugal pumping head fortransmitting a fluid) is positioned adjacent to the rotatingsuperconducting element 106, preferably on a stable support surface Tfabricated of a material that does not interfere with the magnetic fieldcreated by the pumping or mixing element 134. As previously noted, thevessel 132 can be a rigid vessel of any shape (open top, sealed havingan inlet or outlet, cylindrical with a hollow center, such as a pipe, oreven a flexible plastic bag (by itself, with rigid inserts, or insertedinto a rigid or semi-rigid vessel)). The only requirement is that thevessel 132 employed is capable of at least temporarily holding the fluidF (or gas) being mixed or pumped.

To create the desired mixing action in this embodiment, a pumping ormixing element 134 is positioned in the vessel 132 and simultaneouslylevitated and rotated by the superconducting element 106. Morespecifically, the first portion of the cryostat 102 a containing thesuperconducting element 106, thermal link 118, and the evacuated chamber108 is rotated as a result of the rotational motion transmitted by theendless belt 128. This rotation causes the pumping or mixing element 134in the vessel 124 to rotate and either pump or mix the fluid F heldtherein. In the case where the chamber 104 is evacuated or insulated,the pumping or mixing element 134 is rotated in a stable, reliablefashion while the desired thermal separation between tie coldsuperconducting element 106 supplying the levitation force. the vessel124, and hence the fluid F, is achieved. The pumping or mixing element134 may include a plurality of mixing blades B (see FIGS. 6 a and 6 b),vanes V (not shown, but see FIG. 7), or like structures to create animpeller. However, again referring back to FIG. 5, a low-profile,disk-shaped pumping or mixing element 134 may also be used to providethe desired mixing action, especially for particularly delicate fluids,such as blood or other types of cell suspensions.

As perhaps best understood by viewing FIGS. 6 a and 6 b together, thepumping or mixing element 134 may include at least two magnets 135 a,135 b, and possibly more than two (see FIG. 20). These magnets 135 a,135 b not only serve to generate the magnetic field that causes thepumping or mixing element 134 to levitate above the superconductingelement 106, but also transmit rotational motion to the pumping ormixing element. As should be appreciated by one of ordinary skill in theart, the magnetic field generated by the magnets 135 a, 135 b should beaxially non-symmetrical relative to the axis of rotation of thesuper-conducting element 106 in order to create the magnetic couplingnecessary to efficiently transmit the rotary motion. In one embodiment,the magnets 135 a, 135 b are disk-shaped and polarized along a centervertical axis (see FIG. 6 b, showing permanent magnets 135 a, 135 b ofalternating polarities (N—North; S—South) levitating above a pair ofsuperconducting elements 106 a, 106 b, with the corresponding actionarrows denoting the direction and axis of polarity). These magnets 135a, 135 b can be fabricated form a variety of known materials exhibitingpermanent magnetic properties, including, but not limited to,Neodymium-Iron-Boron (NdFeB), Samarium Cobalt (SmCo), the composition ofaluminum, nickel, and cobalt (Alnico), ceramics, or combinationsthereof. The magnets 135 a, 135 b may be interconnected by a piece of aninert matrix material M, such as plastic or inert, non-corrosive metals.Alternatively, the magnets 135 a, 135 b may each be embedded in separatepieces of a matrix material M, or may be embedded in a single unitarypiece of material (not shown). Also, as previously mentioned, thepumping or mixing element 134 may early one or more optional blades B,vanes or like structures to enhance the degree of pumping or mixingaction created.

In another possible embodiment, the second portion of the cryostat 102 bincluding the cooling source (either a liquid cryogen container (opentop, scaled with inlet/outlet ports, or a refrigeration (preferably a“cryocooler,” as described further below)) may be rigidly attached tothe first portion 102 a and both components may be simultaneouslyrotated together (see the dashed lines at the top of the open codlingcontainer 119 in FIG. 5, and see also the embodiment described below andshown in FIGS. 20-21). The rotational motion may be supplied by anendless belt/motor combination, as described above, or alternatively maybe provided through a direct coupling between the second portion of thecryostat 102 b (comprising any type of cooling source) and an inlineshaft extending from or coupled to a motor or similar motive device (notshown).

As briefly mentioned above, it is possible to use this embodiment of thesystem 100 without evacuating, insulating, or otherwise thermallyseparating the superconducting element 106 from the ambient environment,such as for mixing or pumping cold (cryogenic) or non-temperaturesensitive fluids. In that case, there is no specific need for a wall 104or chamber 108 surrounding the superconducting element 106, sincethermally separating it from the structure supporting the vessel 132(e.g., a table, stand or the like) is unnecessary. Even with thismodification, reliable and stable levitation of the pumping or mixingelement 134 is still achieved.

From the foregoing, it should be appreciated that the same drivingmechanism and cryostat shown in FIG. 5 can be used for pumping a fluidinstead of mixing it. One version of a vessel 132 in the form of acentrifugal pumping head 150 is shown in FIG. 7. This pumping head 150includes a pumping chamber 152 having an inlet 154 and an outlet 156(which of course, could be reversed, such as in a non-centrifugalpumping head (see FIG. 2)). The chamber 150 contains the levitatingpumping or mixing element 158, which as shown may include a plurality ofvanes V, or may alternatively carry a plurality of blades (not shown).At least two permanent magnets 160 a, 160 b having different polaritiesare embedded or otherwise included in the pumping or mixing element 158,which may be substantially comprised of an inert matrix material Mhaving any desired shape to facilitate the pumping or mixing action. Asdescribed above, these magnets 160 a, 160 b provide both levitation andtorque transmission as a result of the adjacent rotating superconductingelement 106.

As should be appreciated, one advantage of providing the driving forcefor the levitating pumping or mixing element 158 from the same side ofthe vessel/pumping head 150 from which the levitating force originatesis that the fluid inlet 154 (or outlet 156, in the case where the twoare reversed) may be placed at any location along the opposite side ofthe vessel/pumping head 150, including even the center, withoutinterfering with the pumping or mixing operation. Also, this same sideof the vessel/pumping head 150 may be frusto-conical or otherwiseproject outwardly, as illustrated, without interfering with the rotationor necessitating a change in the design of the pumping or mixing element134, 158.

As briefly noted above, in some instances the opening in a vessel may betoo small to permit an even moderately sized pumping or mixing element134 to be inserted into the fluid F. In such a case, alternate versionsof a pumping or mixing element 134 meeting this particular need areshown in FIGS. 5 a-5 c. In the first alternate version, the pumping ormixing element 134 a is in the form of a slender rod formed of an inertmatrix material M carrying one of the levitating/driven magnets 135 a,135 b at or near each end. As should be appreciated, this pumping ormixing element 134 a may be easily turned to an upstanding position andinserted in the opening. Upon then coming into engagement with therotating superconducting element 106, the pumping or mixing element 134a would simultaneously levitate and rotate to pump or mix a fluid heldin the vessel. To further facilitate insertion in the narrow opening,the matrix material M may be an elastomeric material or another materialhaving the ability to freely flex or bend.

A second version of a pumping or mixing element 134 b for use with avessel having a narrow opening is shown in FIG. 8 b. The pumping ormixing element 134 h includes first and second thin rods 180 formed of amatrix material M. The rods 180 each carry the levitating/driven magnets135 a, 135 b at each end thereof, with at least two magnets having theidentical polarity being held on each different rod. In one version, therods 180 are pinned about their centers (note connecting pin 182) andare thus capable of folding in a scissor-like fashion. As should beappreciated from FIG. 5 c, this allows the pumping or mixing element 134b to be folded to a low-profile position for passing through the openingof the vessel 132. The rods 180 of the pumping or mixing element 134 bmay then separate upon coming into engagement with an appropriatelyfield cooled superconducting element 106 positioned adjacent to thebottom of the vessel 132. Since magnets 135 a or 135 b having the samepolarity are positioned adjacent to each other, the corresponding endsof the rods 180 repel each other as the pumping or mixing element 132 brotates. This prevents the rods 180 from assuming an aligned positiononce in the vessel 132. As should be appreciated, instead of pinning twoseparate rods 180 together to form the pumping or mixing element 134 b,it is also possible to integrally mold the rods 180 of a flexiblematerial to form a cross. This would permit the rods 180 of the pumpingor mixing element 134 b to flex for passing through any narrow opening,but then snap-back to the desired configuration for levitating above thesuper-conducting element 106.

In accordance with yet another aspect of the present invention, a thirdversion of a pumping or mixing system 200 is disclosed. In this thirdembodiment, which is illustrated in FIGS. 9, 9 a, 9 b, and 10, theforces for driving and levitating the pumping or mixing element 204 aresupplied form the same side of a fluid vessel 202 (which is shown as anopen-top container, but as described above, could be a sealed container,a pumping chamber or lead, a flexible bag, a pipe, or the like). In thissystem 200, the pumping, or mixing element 204 actually includes twomagnetic subsystems: a first one that serves to levitate the pumping ormixing element 204, which includes a first magnet 206, preferably in theform of a ring, and a second magnetic subsystem that includes at leasttwo alternating polarity driven magnets 208 a, 208 b, preferablypositioned inside of the first, ring-shaped magnet 206, to transmitdriving torque to the pumping or mixing element (see FIGS. 9 a and 9 b).

FIG. 9 shows one embodiment of the overall system 200 in which thering-shaped permanent magnet 206 or array of magnets (not shown)provides the levitation for the pumping or mixing element 204.Polarization of the ring magnet 206 is vertical (as shown by the longvertical arrows in FIG. 9 b). The driven magnets 208 a, 208 b are shownas being disk-shaped and having opposite or alternating polarities (seecorresponding short action arrows in FIG. 9 b representing the oppositepolarities) to form a magnetic coupling and transmit the torque to thelevitating pumping or mixing element 204. Levitation magnet 206 anddriven magnets 208 a, 208 b are preferably integrated in one rigidstructure such as by embedding or attaching all three to a lightweight,inert matrix material M, such as plastic or the like.

To correspond to the ring-shaped levitation magnet, the superconductingelement 210 for use in this embodiment is annular, as well. This element210 can be fabricated of a single unitary piece of a high-temperaturesuperconducting material (YBCO or the like), or may be comprised of aplurality of component parts or segments. Upon being cooled to thetransition temperature in the presence of a magnetic field and aligningwith the ring-shaped permanent magnet 206 producing, the same magneticfield, the superconducting ring 210 thus provides the combinedrepulsive/attractive, spring-like pinning force that levitates thepumping or mixing element 204 in the vessel 202 in an exceptionallystable and reliable fashion. In FIG. 9, the vessel is shown as beingsupported on the outer surface of a special cryostat 220 designed foruse with this system 200, a detailed explanation of which is provided inthe description that follows. However. it is within the broadest aspectsof the invention to simply support the vessel 202 on any stable supportstructure, such as a table (not shown), as long as it remainssufficiently close to the superconducting element 210 to induce thedesired levitation in the pumping or mixing element 204 held therein.

As in the embodiments described above, a motive device is used to impartrotary motion to the pumping or mixing element 204, and is preferablypositioned adjacent to and concentric with the annular super-conducting,element 210. One example of a motive device for use in the system 200 ofthis third embodiment includes driving magnets 212 a, 212 b thatcorrespond to the driven magnets 208 a, 208 b on the pumping or mixingelement 204 and have opposite polarities to create a magnetic coupling(see FIG. 9 b). The driving magnets 212 a, 212 b are preferably coupledto a shaft 214 also forming part of the motive device. The drivingmagnets 212 a, 212 b may be attached directly to the shaft 214, or asillustrated in FIG. 9, may be embedded or attached to a matrix material(not numbered in FIG. 9, but see FIG. 9 b). By positioning the drivingmagnets 212 a, 212 b close to the pumping or mixing element 204, such asby inserting them in the opening or bore 219 defined by the annularsuperconducting element 210, and rotating the shaft 214 using a motor216 also forming a part of the motive device, synchronous rotation ofthe levitating pumping or mixing element 204 is induced. The pumping ormixing clement 204 may include one or more blades B that are rigidlyattached to the ring or levitation magnet 206 (or any matrix materialforming the periphery of the pumping or mixing element 204). However, itremains within the broadest aspects of the invention to simply use asmooth, low-profile pumping or mixing element (see FIG. 5) to providethe desired mixing action.

As shown in FIGS. 9 and 10 and briefly mentioned above, the mixing orpumping system 200 including the pumping or mixing element 204 comprisedof the magnetic levitation ring 206 and separate driven magnets 208 a,208 b may use a special cryostat 220 to ensure that reliable and stablerotation/levitation is achieved. As perhaps best shown in thecross-sectional side view of FIG. 9, the cryostat 220 includes a coolingsource 221 for indirectly supplying the necessary cooling to thesuperconducting element 210, which as described below is supported andcontained in a separate portion of the special cryostat 220. In theillustrated embodiment, the cooling source 221 (not necessarily shown toscale in FIG. 9) includes a container 222, such as a double-walled Dewarflask, in which a first chamber 224 containing a liquid cryogen C(nitrogen) is suspended. A second chamber 223 defined around the firstchamber 224 is preferably evacuated or insulated to minimize thermaltransfer to the ambient environment, which is normally at roomtemperature. A port 226 is also provided for filling the suspendedchamber 224 with the chosen liquid cryogen C, as well as for possiblyallowing any exhaust gases to escape. As with the first and secondembodiments described above, the cooling source 221 may instead take theform of a closed-cycle refrigerator (not shown), in which case thedouble wall container 222 may be entirely eliminated from the system200.

A thermal link 228 is provided between the cooling source (in theillustrated embodiment, the container 222) and a platform 230 suspendedin the cryostat 220 for supporting the superconducting ring 210. The useof the platform 230 is desirable to ensure that the temperature of thesuperconducting element 210 is kept below the transition temperature,which in the ease of a “high temperature” superconducting material (suchas YBCO) is most preferably in the range of between 87-93 Kelvin.However, the use of the platform 230 is not critical to the invention orrequired as part of the special cryostat 220, since the thermal link 228could extend directly to the superconducting element 210. The thermallink 228 may be a solid rod of material, including copper, brass, or anyother material having a relatively high thermal conductivity. Instead ofa solid rod, it is also possible to provide an open channel 232 in thethermal link 228, especially when a liquid cryogen C capable of flowingfreely, such as nitrogen, is used as the cooling source 221. Thischannel 232 allows the cryogen C from the suspended container 224 toreach the platform 230 directly. Of course, the direct contact with thecryogen C may provide more efficient and effective cooling for thesuperconducting element 210, but is not required.

The ring-shaped platform 230 that supports the superconductingelement(s) 210 and supplies the desired cooling via thermal conductionmay be made of copper, brass, aluminum. or another material having goodthermal conductivity. It may be in the form of a solid ring, asillustrated, or may be in the form of a hollow ring (such as asubstantially circular or elliptical torus, not shown). This would allowthe liquid cryogen C to flow completely around the ring to furtherincrease the efficiency with which the cooling is transferred to thesuperconducting element 210. In any case, where a platform 230 is used,care should be taken to ensure that full contact is made with at least amajority of the corresponding surface of the superconducting element210, since even cooling helps to ensure that the desired smooth, even,and reliable levitation is achieved.

To reduce the thermal transfer to the vessel 202 in tie case where atemperature sensitive fluid is being pumped or mixed by the system 200,a ring-shaped wall or enclosure 234 surrounding the platform 230 and theannular superconducting element 210 defines a first chamber 235. Inaddition, a hollow cylindrical wall or enclosure 236 may also surroundthe thermal link 232 and define a second chamber 237. Preferably, thesefirst and second chambers 235, 237 are evacuated or insulated tominimize thermal transfer between the ambient environment and the coldelements held therein. In a preferred embodiment, each enclosure 234,236 is fabricated from nonmagnetic stainless steel, but the use of othermaterials is of course possible, as long as no interference is createdwith the levitation of the pumping or mixing element 204. As with thesecond embodiment described above, it is also possible to use the system200 of the third embodiment to pump or mix cryogenic or non-temperaturesensitive fluids, in which case there is no need to evacuate or insulatethe enclosures 234, 236, or to even use the special cryostat 220described herein.

As should be appreciated, it is possible to create the chambers 235, 237defined by the enclosures 234, 236 and the chamber 223 such that allthree are in fluid communication and thus represent one integratedvacuum space (not shown). This facilitates set-up, since all threechambers 223, 235, 237 may be evacuated in a single operation, such asby using a vacuum source coupled to a single valve (not shown) providedin one of the chambers. However, separately evacuating each chamber 223,235, 237 is of course entirely possible. Also, instead of or in additionto evacuating the chambers 223, 235, 237, some or all may be insteadfilled with a suitable insulating material (not shown).

As should be appreciated, to rotate the pumping or mixing element 204 inthis embodiment, it is desirable to place the drive magnets 212 a, 212 bin close proximity to the pumping or mixing element, but preferably onthe same side of the vessel 202 as the superconducting element 210.Accordingly, the special cryostat 220, and more specifically, the wallor enclosure 234 defines a room-temperature cylindrical bore or opening240 that allows for the introduction of the end of the shaft 214carrying the driving magnets 212 a, 212 b, which are at roomtemperature. As a result of this arrangement, the shaft 214, which ispart of the motive device, is concentric with the superconductingelement 210. The shaft 214 is also positioned such that the drivingmagnets 212 a, 212 b align with the driven magnets 208 a, 208 b on thepumping or mixing element 204 when the levitating magnet 206 is alignedwith the superconducting element 210. Thus, despite being positionedadjacent to and concentric with the superconducting element 210. theshaft 214 and driving magnets 212 a, 212 b remain at room temperature,as does the vessel 202, the fluid F, and the pumping or mixing element204.

An example of one possible embodiment of a centrifugal pumping head 250for use with the system 200 of FIG. 9 is shown in FIG. 11. The head 250includes a levitating pumping or mixing element 252 that carries one ormore optional blades or vanes V (which are upstanding in the side viewof FIG. 11), a fluid inlet 254 (which as should be appreciated can be inthe center at one side of the pumping head 250 in view of the fact thatthe levitation and driving forces are both supplied from the same sideof the vessel 202), a fluid outlet 256, driven magnets 258 a, 258 b, anda ring-shaped levitation magnet 260.

In yet another possible embodiment of the invention, as shown in thecross-sectional view of FIG. 12, the system 300 includes a pumping ormixing element 302 adapted for inline use, such as when the vessel is inthe form of a hollow pipe 304. The pumping or mixing element 302includes first and second spaced levitating magnets 305 a, 305 h, one ofwhich is preferably positioned at each end to ensure that stablelevitation is achieved. The magnets 305 a, 305 b preferably correspondin shape to the vessel, which in the case of a pipe 304, means that theyare annular. The magnets 305 a, 305 b are carried on a shaft 306 forminga part of the pumping or mixing element 302, which further includes adriven magnet 308. The driven magnet 308 may be comprised of a pluralityof sub-magnets 308 a . . . 308 n having different polarities andarranged in an annular configuration to correspond to the shape of thepipe 304 serving as the vessel in this embodiment (see FIG. 12 b). Allthree magnets 305 a, 305 b, and 308 may be embedded or attached to aninert matrix material M, such as plastic, that provides the connectionwith the shaft 306. The shaft 306 of the bearing 302 may also carry oneor more blades B.

First and second “cryostats” 310 a, 310 b are also provided. As perhapsbest understood with reference to the cross-sectional view of FIG. 12 a,the first “cryostat” 310 a includes a superconductor for levitating thepumping or mixing element in the form of an annular superconductingelement 312 a. This superconducting element 312 a is suspended in achamber 314 a defined by the cryostat 310 a, which may be evacuated orinsulated to prevent thermal transfer to the pipe 304 or the passingfluid F. The cryostat 310 a may include an inner wall adjacent to theouter surface of the pipe 304 (not shown), but such a wall is notnecessary in view of the thermal separation afforded by the evacuated orinsulated space surrounding the superconducting element 312 a. Thesuperconducting element 312 a may be coupled to annular support platform316 a, which in turn is thermally linked to one or more separate coolingsources 318. The connection is only shown schematically in FIG. 12 butas should be appreciated from reviewing the foregoing disclosure, mayinclude a rod that serves to thermally link a container holding a liquidcryogen or a closed cycle refrigerator to the superconducting element312 a. While not shown in detail, “cryostat” 310 b may be similar oridentical to the cryostat 310 a just described.

With reference now to FIGS. 12 b and 12 c, two different motive devicesfor rotating the pumping or mixing element 302 in the pipe 304 aredisclosed. The first motive device includes a driving magnet assembly320 that is rotatably supported on a bearing 322, such as a mechanicalball or roller bearing, carried on the outer surface of the pipe 304.The magnet assembly 320 includes a plurality of driving magnets 320 a .. . 320 n, also having different or alternating polarities. As with thedriven magnets 308 a . . . 308 n, the driving magnets 320 a . . . 320 nare embedded or attached to an inert, nonmagnetic matrix material A,such as plastic. An endless belt 324 also forming a part of the motivedevice functionally engages both the driving magnet assembly 320 and apulley or wheel W carried on the spindle or shaft of a motor (preferablya reversible, variable speed electric motor, as described above).

As should now be appreciated, the pumping or mixing element 302 iscaused to levitate in the pipe 304 as a result of the interaction of thelevitation magnets 305 a, 305 b with the adjacent superconductingelements 310 a, 310 b, which may be thermally separated from the outersurface of the pipe 304 (or the adjacent inner wall of the cryostat 310a, 310 b, if present). Upon then rotating the magnetic drive assembly320, the pumping or mixing element 302 is caused to rotate in the pipe304 serving as the vessel to provide the desiring pumping or mixingaction. Even if the fluid F is flowing past the pumping or mixingelement 302, it remains held in place in the desired position in thepipe 304 as a result of the pinning forces created by thesuperconducting elements 310 a, 310 b acting on the levitation magnets305 a, 305 b.

The second version of a motive device is shown in the cross-sectionalview of FIG. 12 c, which is similar to the cross-section taken in FIG.12 b. However, instead of a magnetic driving assembly 320, endless belt324, and motor, rotary motion is imparted to the pumping or mixingelement 302 by creating an electrical field around the pipe 304. Thismay be done by placing a winding 326 around the outer wall of the pipe304 and supplying it with an electrical current, such as from a powersupply 328 or other source of AC current. Since the pumping or mixingelement 302 carries magnets 305 a . . . 308 n having differentpolarities, the resulting electric field will thus cause it to rotate.

Yet another embodiment of an inline pumping or mixing system 400 isshown in FIG. 13. The cryostat 402 in this case is essentiallypositioned directly in the path of fluid flow along the pipe 403, thuscreating an annular (or possibly upper and lower) flow channels 404 a,404 b. The cryostat 402 has an outer wall 406 that defines a chamber 408for containing a superconducting element 410. The super-conductingelement 410 may be annular in shape, in which case the chamber 408 is ofa similar shape. The chamber 408 may also be evacuated or insulated tothermally separate the superconducting element 410 from the outer wall406. The superconducting element 410 is thermally linked to a separatecooling source 412, with both the thermal link and the cooling sourcebeing shown schematically in FIG. 13. It should be appreciated that thiscryostat 402 is similar in many respects to the one described above indiscussing the third embodiment illustrated in FIG. 9, which employs asimilar, but somewhat reoriented, arrangement.

The wall 406 creating annular chamber 408 for the superconductingelement 410 defines a room temperature bore or opening 414 into which aportion of a motive device may be inserted, such as the end of a shaft416 carrying at least two driving magnets. FIG. 13 illustrates themotive device with three such driving magnets 418 a, 418 b, 418 c one ofwhich is aligned with the rotational axis of the shaft 416. The oppositeend of the shaft 416 is coupled to a motor (not numbered), which rotatesthe shaft and, hence, the driving magnets 418 a, 418 b, and 418 c. Themagnets 418 a, 418 b, 418 c may be coupled directly to the shaft 416, orembedded/attached to an inert matrix material M.

The pumping or mixing element 420 is positioned in the pipe 403 adjacentto the outer wall 406 of the cryostat 402. The pumping or mixing element420 includes a levitation magnet 422 that corresponds in size and shapeto the super-conducting element 410, as well as driven magnets 424 a,424 b, 424 c that correspond to the driving magnets 418 a, 418 b, and418 c. The levitation magnet 422 and driven magnets 424 a-424 c areattached to or embedded in a matrix material M, which may also supportone or, more blades B that provide the desired pumping or mixing action.

In operation, the motor rotates the shaft 416 to transmit rotary motionto the driving magnets 418 a, 418 b and 418 e. As a result of themagnetic coupling formed between these magnets 418 a-c and the oppositepolarity driven magnets 424 a-c, the pumping or mixing element 420 iscaused to rotate in the fluid F. At the same time, the pumping or mixingelement 420 remains magnetically suspended in the fluid F as the resultof the pinning forces created between the superconducting element 410and the levitation magnet 422. The operation is substantially the sameas that described above with regard to the third embodiment, and thuswill not be explained further here.

Various optional modifications may in some circumstances enhance theset-up or performance of any of the systems described herein, or insteadadapt them for a particular use, purpose, or application. As notedpreviously, the disposable vessel or container for holding the fluidundergoing pumping or mixing may be in the form of a flexible bag. Anexample of such a bag 500 is shown in FIG. 14, along with the system 100for levitating the pumping or mixing element 502 of FIG. 5. The bag 500may be sealed with either fluid F or the pumping or mixing element 502(which may take the form of one of the several pumping or mixingelements disclosed above or an equivalent thereof inside prior todistribution for use, or may be provided with a sealable (or resealable)opening that allows for the fluid and pumping or mixing element to beintroduced and later retrieved.

Both the pumping or mixing element 502 and bag 500, whether permanentlysealed or resealable, may be fabricated of inexpensive, disposablematerials. Accordingly, both can simply be discarded after the pumpingor mixing operation is completed and the fluid F is retrieved. It shouldalso be appreciated that the vertical dimension of the bag 500 isdefined by the volume of fluid F held therein. Thus, instead of placingthe bag 500 containing the pumping or mixing element 502 directly on thesurface of the cryostat, table T, or other support structure adjacent tothe superconducting element 106, it is possible to place the flexiblebag 500 in a separate rigid or semi-rigid container (see, e.g., FIG.22). This helps to ensure that the fluid F provides the bag 500 with asufficient vertical dimension to permit the pumping or mixing element502 to freely rotate in a non-contact fashion. Alternatively, the bag500 may include internal or external reinforcements (not shown) toenhance its rigidity without interfering with the rotation of thepumping or mixing element.

In cases where the pumping or mixing element 502 is prepackaged in thebag 500, with or without fluid, it may inadvertently couple to adjacentmagnets or other metallic structures. Breaking this coupling may renderthe bag susceptible to puncturing, tearing. or other forms of damage.Accordingly, as shown in FIGS. 14 a and 14 b, it may be desirable tohold the pumping or mixing element 502 place prior to use with any ofthe systems described herein, especially in cases where it is sealedinside the vessel/bag 500 during manufacturing

As shown in FIG. 14 a, one manner of holding the element 502 in place isto use an attachment 520, cover, or similar device including a coupler522 formed of a ferromagnetic material or the like adjacent to the bag500. This coupler 522 is thus attracted to and forms a magnetic couplingwith the pumping or mixing element 502 when the attachment 520 is inplace. As a result of this coupling, the pumping or mixing element 502is prevented from coupling with magnets in adjacent bags or othermagnetic structures (not shown). The attachment 520 should be fabricatedof a non-magnetic material, such as rubber. In the operative position,the coupler 522 shields the magnetic field created by the plumping ormixing element 502. When the assembly including the bag 500 and thepumping or mixing element 502 is ready for use, the attachment 520 maysimply be removed from the bag 500 to break the magnetic couplingbetween the pumping or mixing element 502 and the coupler 522.

A second manner of keeping the pumping or mixing element 502 at adesired location to facilitate coupling with the particularlevitation/rotation devices used is to provide the bag 500 with acentering structure, such as a post 528. As shown in the embodimentillustrated in FIG. 14 b, which includes the basic levitation androtation system of FIG. 5, this post 528 may take the form of a rigid orsemi-rigid piece of material projecting into the interior of the bag500. Preferably, the post 528 is formed of the same material as the bag500 or other container (plastic) and has an outer diameter that is lessthan the inner diameter or a bore or opening formed in the pumping ormixing element 502. As should be appreciated, the pumping or mixingelement 502 may be held in place on the post 528 by gravity duringshipping prior to use, and even between uses. As illustrated the upperend of the post 528 could also include a T-shaped or oversized head 529(which could have a spherical, pyramidal, conic, or cubic shape).Alternatively, the head could have one or more transversely extending,deformable cross-members, an L-shaped hook-like member, or another typeof projection for at least temporarily capturing the pumping or mixingelement 502 to prevent it from inadvertently falling off when not inuse. Of course, the positioning of the head 529 for capturing thepumping or mixing element 502 is preferably selected such that it doesnot interfere with the free levitation or rotation. As should beappreciated, the post 528 provides not only centering function, but alsoholds the pumping or mixing element 502 in place in case it accidentallydecouples during the pumping or mixing operation. This significantlyeases the process of returning the pumping or mixing element 502 to theproper position for initiating or resuming levitation/rotation by thecorresponding system (which may be, for example, systems 10, 100, 200,300, 800 etc.).

In FIG. 14 b, this post 528 is adapted to receive the pumping or mixingelement 502, which has a corresponding opening (and thus, may be annularor have any other desired shape or size). Since the post 528 preferablyincludes an oversized head portion 529 that keeps the pumping or mixingelement 502 in place, including before a fluid is introduced, the vessel500 may be manufactured, sealed (if desired), shipped, and stored priorto use with the pumping or mixing element 502 already in place. Thevessel 500 may also be sterilized as necessary for a particularapplication, and in the case of a flexible bag, may even be folded forcompact storage. As should be appreciated, the post 528 also serves theadvantageous function of keeping the pumping or mixing element 502substantially in place (or “centered”) should it accidentally becomedecoupled from the adjacent motive device, which as in this case is arotating annular superconducting element 106. However, the centeringpost 528 could also be used in the embodiment of FIG. 9 as well bysimply forming a center opening in the pumping or mixing element 204.

In the illustrated embodiment, the post 528 is shown as being formed byan elongated rod-like structure inserted through one of the nipples 530typically found in the flexible plastic bags frequently used in thebioprocessing industry (pharmaceuticals, food products, cell cultures,etc.). The oversized head portion 529 is preferably formed of a materialthat is sufficiently flexible/deformable to easily pass through theopening in the nipple 530. A conventional clamp 531, such as a cable orwire tie, may be used to form a fluid-impervious seal between the nipple530 and the portion of the post 528 passing therethrough, but otherknown methods for forming a permanent or semi-permanent seal could beused (e.g., ultrasonic welding in the case of plastic materials,adhesives, etc.). Any other nipples 530 present (shown in phantom inFIG. 14 b) may be used for introducing the fluid prior to mixing,retrieving a fluid during mixing or after mixing is complete, orcirculating the fluid in the case of a pumping operation.Advantageously, the use of the rod/nipple combination allows for easyretrofitting. Nevertheless, instead of using a separate rod, the post528 may be integrally formed with the material forming the vessel 500,either during the manufacturing process or as part of a retrofitoperation. Also, as noted in my prior applications, the oversized headportion 529 may be cross-shaped, disc-shaped, L-shaped, Y-shaped, or mayhave any other desired shape, as long as the corresponding function ofcapturing the pumping or mixing element 502 is provided. The headportion 529 may be integrally formed, or alternatively may be providedas a separate component that is clamped or fastened to the post 528.

In yet another embodiment, the vessel 500 may also include a structurethat helps to ensure that proper alignment is achieved between thecentering post 528 and an adjacent structure, such as a device forrotating and/or levitating the pumping or mixing element 502. In theembodiment of FIG. 14 b, this alignment structure is shown in the formof an alignment post 532 projecting outwardly from the vessel 500 andco-extensive with the centering post 528. The post 532 extends throughan opening 536 formed in the lower portion, such as the floor, of asemi-rigid support container 534 defining a compartment for receivingthe vessel 500. The container 543 thus serves as a support structure(which may instead be the table T, as shown in FIG. 14 e).

The adjacent motive device, which as shown as including a cryostat 102containing a rotating superconducting element 106, includes a locatorbore 533. This bore 533 is concentric with the superconducting element106 and is sized and shaped for receiving the alignment post 532 (whichmay have any desired cross-sectional shape, including circular,elliptical. square., polygonal, etc.). As a result of the centering andalignment posts 528, 532, assurance is thus provided that the pumping ormixing element 502 is in the desired position for forming a couplingwith an adjacent motive device, such as the cryostat 102 housing therotating superconducting element 106 (which may both rotate together, asdescribed above). This is particularly helpful for properly aligning thepumping or mixing element 502 with the cryostat, such as cryostat 102,in the case of opaque vessels or adjacent containers, sealed or asepticcontainers, large containers, or where the fluid is not clear. Insteadof forming the alignment post 532 firm an elongated rod inserted into anipple 530 or the like, it should be appreciated that it may also beintegrally formed with the vessel 500 during manufacturing, or laterduring a retrofit.

FIG. 14 b also shows the centering post 528 projecting upwardly fi-on abottom wall of the vessel 500, but as should be appreciated it couldextend from any wall or other portion thereof. For example, asillustrated in FIG. 14 c, the rod serving as both the centering post 528and the alignment post 532 may be positioned substantially perpendicularto a vertical plane. Specifically, in the particular embodiment shown,the vessel 500 is an empty flexible bag as shown above positioned in arigid or semi-rigid support container 534 having an opening 536 formedin the lower portion thereof. Once the vessel 500 is inserted in thecontainer 534, but preferably prior to introducing a fluid, thealignment post 532 is positioned in the opening 536 such that itprojects therefrom (along with any inlet or outlet hoses present). Theproximal end of the alignment post 532 is then inserted into acorresponding receiver in the motive device, such as the locator bore533 formed in the cryostat 102 (which is easily reoriented, as describedherein). This ensures that the pumping or mixing element 502 is in thedesired position to form the magnetic coupling with the superconductingonce field cooling is complete to achieve levitation and/or rotationwithout the need for external intervention. As noted above, the couplingmay be formed either before or after the introduction of the fluid intothe vessel 500. Also, while shown in conjunction with a particularembodiment of the pumping or mixing system, it should be appreciatedthat the alignment and centering posts 528, 532 may, either together orseparately, be used in conjunction with different types of pumping ormixing elements or with any of the pumping or mixing systems disclosedherein.

In many of the above-described embodiments, the pumping or mixing actionis essentially localized in nature. This may be undesirable in somesituations, such as where the vessel is relatively large compared to thepumping or mixing element. To solve this problem, the particular systemused to supply the pumping or mixing action may be provided with amotive device for physically moving the superconducting element (whichmay also be simultaneously rotated). This of course will cause thelevitating pumping or mixing element to follow a similar path.

With reference to the schematic view of FIG. 14 d, and by way of exampleonly, the particular arrangement is shown in use on the system 100 ofFIG. 5, but with the bag 500 of FIG. 14. In addition to a motive device540 for rotating the first portion of the cryostat 102 a (which maycomprise the bearing(s) 120, endless belt 128, motor 131, shaft, andpulley) and a cooling source 541, the system 100 may include a secondmotive device 542. In one embodiment, this second motive device 542(shown schematically in dashed line outline only in FIG. 14 c) iscapable of moving the first portion of the cryostat 102 a, and hence thesuperconducting element 106, to and fro in a linear fashion (see actionarrow L in FIG. 14 c). Thus, in addition to levitating and rotating thepumping or mixing element 502, the side-to-side motion allows it to moverelative to the bag 500 or other vessel containing the fluid. Thisadvantageously permits non-localized pumping or mixing action to beprovided. The second motive device 542 may include a support structure,such as a platform (not shown) for supporting all necessary components,such as the first portion of the cryostat 102 a (or the entire cryostat,such as in the embodiment of FIG. 9), the first motive device 540 forrotating one of the superconducting element 106 (or the pumping ormixing element 502 such as in the embodiment of FIG. 9), and the coolingsource 541 (which may form part of the cryostat as shown in FIG. 9, ormay be a separate component altogether, as shown in FIG. 2). Instead ofusing a linear motion device, it should also be appreciated that thesecond motive device 542 may be capable of moving the superconductingelement 106 in a circular or elliptical path relative to the fixedposition of the bag 500 or other vessel, or in any other direction thatwill enhance the overall mixing or pumping action provided by therotating pumping or mixing element 502. Also, the bag 502 or vessel maybe separately rotated or moved to further enhance the operation (see theabove-description of the embodiment of FIG. 3).

Ensuring that the pumping or mixing elements are both proper for aparticular system and are of the correct shape and size may also beimportant. To do so, it is possible to provide a transmitter in one ofthe pumping or mixing element or the vessel for generating a signal thatis received by a receiver in the system (or vice versa), such as onepositioned adjacent to the superconducting element or elsewhere. Anexample of one possible configuration is shown in FIG. 14, wherein thetransmitter 550 is provided on the pumping or mixing element 502 itselfand the receiver 560 is positioned in the cryostat 102 (but see FIG. 14a, wherein the transmitter 550 or receiver 560 is provided in the bag500 serving as the vessel). A controller for the system, such as acomputer (not shown) or other logic device, can then be used to maintainthe system for rotating the pumping or mixing element 502 in anon-operational, or “lock-out.” condition until the receiver andtransmitter 550, 560 correspond to each other (that is, until thetransmitter 550 generates an appropriate signal that is received by thereceiver 560). The transmitter/receiver combination employed may be ofany type well known in the art, including electromagnetic, ultrasound,optical, or any other wireless or remote signal transmitting andreceiving devices.

In accordance with another aspect of the invention, a kit is alsoprovided to assist in the set-up of any of the systems previouslydescribed. Specifically, and as briefly noted in both this and my priorapplications, it is necessary during field cooling to cool thesuperconducting element to below its transition temperature in thepresence of a magnetic field in order to induce levitation in apermanent magnet producing the same magnetic field. This cooling processcauses the superconducting element to “remember” the field, and thusinduce the desired levitation in the pumping or mixing element each timeit or any other magnet having either a substantially similar oridentical magnetic field distribution is placed over the superconductingelement. While it is possible to use the pumping or mixing elementitself to produce the magnetic field required during field cooling,oftentimes the pumping or mixing element will be sealed in the vessel orcontainer. This makes it difficult, if not impossible, to ensure thatthe magnets held therein are properly aligned and spaced from thesuperconducting element during field cooling.

One way to overcome this potential problem is to use a set-up kit. Asillustrated in FIG. 15, the set-up kit may comprise at least onecharging magnet 600 having a size, shape, and magnetic fielddistribution that is identical to the levitation magnet contained in theparticular pumping or mixing element slated for use in one of thepumping or mixing systems previously described. The charging magnet 600is placed adjacent to the superconducting element 602, such as on theupper surface of the cryostat 604, table (not shown), or otherstructure. As illustrated, the charging magnet 600 may further include aspacer 606. This spacer 606 allows the charging magnet 600 to simulatethe spacing of the pumping or mixing element (not shown) above thesuperconducting element 602 during field cooling. This ensures that thedesired levitation height is achieved for the pumping or mixing element(not shown) once the vessel is in position. The spacer 606 is formed ofa non-magnetic material to avoid interfering with the charging process.By providing a variety of different sizes, shapes, and configurations ofcharging magnets in the kit (e.g., annular magnets), it is possible toeasily perform field cooling for any corresponding size or shape oflevitation magnet in the corresponding pumping or mixing element, andthen simply place the vessel containing the pumping or mixing elementover the superconducting element 602 to induce the desired stable,reliable levitation. It is also possible to field cool thesuperconducting element 602 while the cryostat 604 is in oneorientation, and then reorient it for forming the coupling with thepumping or mixing element (see, e.g., FIG. 14 c).

During field cooling, and regardless of whether the pumping or mixingelement or a separate charging magnet 600 is used to produce thecharging magnetic field, it is possible to unintentionally oraccidentally induce an undesired magnetic state in the superconductingelement 602, such as if the position of the pumping or mixing element(not shown) or charging magnet 600 is not correct. Since impropercharging may prevent the pumping or mixing element from levitating in astable fashion, recharging the superconducting element 602 may berequired. To facilitate recharging the superconducting element, it isprovided with a heater H, such as an electric heating coil (not shown).By energizing this coil using a power supply P or other source ofelectrical current (not shown), the superconducting element 602 may bequickly brought up from the transition temperature for recharging. Asshown schematically, the power supply P is preferably positionedexternally to the cryostat 604. Once the position of the pumping ormixing element or charging magnet 600 is adjusted or corrected, theheater H may be turned off and the superconducting element once againallowed to cool to the transition temperature in the presence of thedesired magnetic field. Yet another embodiment of a system 700 isprovided for use with a particular type of vessel including a cavity,such as of the type designed to withstand high internal pressures. Evenwith this cavity, the system 700 permits a strong magnetic coupling tobe formed between an external magnet or superconductor and one or moremagnets forming part of an internal mixing element, such as a rotor orimpeller, inside the vessel to ensure that stable, reliable levitationis achieved.

As shown in the schematic, partially cross-sectional side elevationalview of FIG. 16, the vessel 702 includes a cavity 704 formed in onesidewall thereof. As briefly explained above, the shape of this cavity704 is preferably cylindrical. In the cylindrical case, this shapeallows for the outer sidewall of the cavity 704 to be fabricated havinga first thickness t₁ (about 2 millimeters in one possible embodiment,but possibly even less), with the remainder of the vessel 702 beingformed from the same or a different material having a second, greaterthickness t₂ (e.g., more than 2 millimeters, and preferably about 7millimeters). To form a unitary vessel, the cavity 704 may be formed asa separate “hat-shaped” section, including an annular flange that iswelded (see weld 705 in FIG. 16) to a corresponding flange (notnumbered).

With this construction, the vessel 702 is able to withstand relativelyhigh internal pressures (up to about 7 bar, and possibly greater), yetthe relatively thin sidewall of the cavity 704 allows for strongmagnet-magnet/magnet-superconductor interactions to be achieved. Ofcourse, the potential reduction in thickness of the sidewalls of thecavity 704 and the upper limit of the internal pressure are directlyinfluenced by the type of material used with the dimensions providedabove corresponding to a vessel 702 formed of conventional nonmagneticstainless steel. Although a cylindrical cavity 704 is shown, it shouldbe appreciated that other equivalent geometric arrangements may also beused, including those having regular or it-regular polygonalcross-sections or the like.

To adapt the superconducting levitation scheme described immediatelyabove to a vessel 702 having such a cavity 704, a special “cryostat” 706may be used, which is generally similar in construction to the one shownin FIG. 9. In the illustrated embodiment, the cryostat 706 includes anexternal wall 708 that defines an enclosed space or chamber (notnumbered). This space is evacuated, such as by using a vacuum source(not numbered), and together with the wall 708 creates a vacuum “jacket”710 around a superconductor or superconducting element 712 held therein.The superconducting element 712 is preferably a “high temperature”superconducting element formed of melt-textured ReBa₂Cu₃O_(x), with Rerepresenting a rare earth element (e.g., Yttrium, of which YBCO is acommon example), but the use of other such materials either alreadyknown or discovered after the filing is of course possible withoutdeparting from the broadest aspects of the invention. Also, as is knownin the art, the superconducting element 712 may be formed from a singleannular or ring shaped piece of material, or as outlined further in thedescription that follows, may be comprised of a plurality of contiguousor non-contiguous segments or sections, each formed of a piece ofsuperconducting material interconnected or arranged in an annular orsubstantially polygonal configuration.

In the illustrated embodiment, the superconducting element 712 ispositioned in a “head” portion of the cryostat 706 sized and/orotherwise adapted for extending or projecting into the cavity 704 formedin the vessel 702. The cryostat 706 also includes or houses a thermallink 714 for supplying the cooling that keeps the element 712 in thedesired superconducting state. As described above, the thermal link 714is preferably formed of a material having a high degree of thermalconductivity/low thermal resistance (metals, such as copper, brass, orthe like). Although not critical, the link 714 may include an engagementportion corresponding generally in size and shape to the superconductingelement 712 to ensure that the desirable full contact and engagement isestablished between the corresponding surfaces to improve thermaltransfer. As also described above, the thermal link 714 is connected toa cooling source, such as a Dewar flask filled with a liquid cryogen, aclosed cycle refrigerator, or the like (see, e.g., FIG. 9). It should beappreciated by skilled artisans that the particular cooling source orthermal link used is not important or critical, as long as it is capableof maintaining the element 712 in the desired superconducting state toinduce levitation in the mixing element 722.

As with the embodiment in FIG. 9, the outer wall 708 of the cryostat 706may be configured to create a bore or opening that allows for a shaft716 or the like to pass therethrough (see FIG. 16 a). One end of theshaft 716 is coupled to a motive device. such as a motor 718, while theother carries a plurality or array of drive magnets 720. The drivemagnet array 720 is preferably positioned in close proximity to theinside surface of the sidewall of the cavity 704, and is comprised of aplurality of magnets having alternating polarities or polar orientations(with the N-S poles preferably being arranged perpendicular to thevertical plane and spaced sufficiently close to the wall of the cavity704 to create the strongest possible magnetic coupling, and hence, themost efficient torque transfer).

Turning now to the mixing element 722, it is preferably in the form of arotor or impeller comprised of a hollow, substantially cylindrical ortubular body sized so as to permit a concentric orientation with thecylindrical cavity 704 inside the vessel 702. The mixing element 722 maycomprise a levitation magnet 724 generally corresponding in shape andproportional in size to the superconducting element 712, and preferablyhaving its poles oriented in a direction parallel to a vertical plane.Spaced from the levitation magnet 724, and preferably embedded in amatrix material M, is an array of strategically positioned drivenmagnets 726. The driven magnets 726 correspond generally in size andshape to the array of alternating polarity drive magnets 720 carried onthe shaft 716. The driven magnets 726 are also of alternating polarityto create the desired magnetic coupling with the drive magnets 720 fortransmitting the drive torque from the motive device, such as the motor,to the shaft 716, and ultimately to the levitating mixing element 722.As shown in FIG. 16, the mixing element 722 may also carry one or moreblades 728, vanes, or the like to furthers enhance the mixing actionprovided (or pumping action, in the case of a pumping clamber having acavity bottom).

Hence, as depicted in FIG. 16, it is possible to easily adapt the mixingsystem 700 for use with a vessel 702 having a thin-walled cavity 704that is nevertheless capable of withstanding high pressures, such asthose possibly created during cleaning or sterilization. As an exampleof one possible application, the vessel 702 may thus be pre-sealed withthe magnetic mixing element 722 (e.g., rotor or impeller) inside, andthen simply placed over the cryostat 706, such as by positioning thevessel on an adjacent stable support surface, such as a table, supportplatform, stand or the like (see reference character T in FIG. 16).Assuming that field cooling has previously been completed (such as byusing a “kit” for supporting a corresponding “set-up” magnet adjacent tothe superconducting element 712 during cooling, which in this case couldbe an annular set-up magnet, as opposed to the disc-shaped one in FIG.15), the vessel 702 is simply positioned over the cryostat 706, as shownin FIG. 16, such that the magnetic field of the permanent levitationmagnet 724 creates the desired flow of current through thesuperconducting element 712 to achieve the simultaneous attraction andrepulsion that results in stable levitation.

During experimentation using the system 700, it was discovered that itmay be advantageous in terms of levitational stability to form thesuperconducting element 712 of a plurality of segments of themelt-textured/melt-processed rare-earth superconductor described above,with the particular orientation of the crystallographic axis or planesof each segment being selected to significantly enhance the magneticstiffness of the coupling, as well as the load capacity of thelevitating mixing element 722. Specifically, as shown in FIG. 17, whichis a plan schematic view of the levitation magnet 724 and a plurality ofsegments 712 a . . . 712 n formed of a superconducting material havingcrystallographic planes (see below) and arranged in a non-contiguouspolygonal configuration, and FIG. 18, which is a cross-sectional view ofthe same taken along line 18-18 of FIG. 17, the crystallographic“C-axis” of each superconducting segment 712 a . . . 712 n is orientedin a radial direction, or in the illustrated embodiment, substantiallyperpendicular to the magnetization vector of the levitation magnet 724,and preferably passes through the center thereof. Accordingly, the A-Bplanes are oriented substantially parallel to the polar magnetizationaxis of the levitation magnet 724. Superconducting materials havingthese crystallographic planes/axes include those comprised ofReBa₂Cu₃O_(x), formed by a melt-texturing or “melt-processing,” as isknown in the art (see, e.g., U.S. Pat. No. 5,747,426 to Abboud, thedisclosure of which is incorporated herein by reference).

Using this arrangement, it was found that the levitation force, magneticstiffness, and concomitant load capacity of the levitation magnet 724 isincreased on the order of two to three times without a correspondingchange in any other parameter of the system 700 described above. Ofcourse, these increases serve to enhance the rotational stability of themixing element 722 when such an arrangement is used in a pumping ormixing system, which in turn improves the operational reliability. Theseincreases also advantageously reduce the tendency of the pumping ormixing element 722 to decouple at higher rotational speeds or in pumpingor mixing high viscosity fluids or the like.

It is also noted that the system 700 is generally described above as amixing system for use with vessels 702 or containers capable ofwithstanding high pressures. However, it should also be appreciated thatthe system 700 could also be used for the mixing or pumping of fluidsthrough a vessel 702 in the form of a flexible, open-top container orany other type of container having the cavity 704 or a similarconfiguration. Of course, the strategic orientation of the elements of asegmented superconductor could also be used to enhance the levitationaland rotational stability of a pumping or mixing element used in any ofthe systems described herein as well.

Yet another embodiment of a pumping or mixing system 800 is proposed inFIG. 19. Perhaps the best way to describe this embodiment is to beginwith a description of the vessel 810 and the pumping or mixing element812. The vessel 810, like vessel 702, is prefer ably created having acavity 814 that defines a concentric annular protruding portion 815.Preferably, the wall defining each side of cavity 814 and each side ofthe annular portion 815 is fabricated of a relatively thin, non-magneticmaterial, such as stainless steel. As noted above with regard to vessel702, by forming the remainder of the vessel 810 having relatively thicksidewalls, it may withstand high pressures, such as those created duringsterilization using steam under pressure or the like. However, in thecase where the vessel 810 is not subjected to high pressures or is usedas a pumping chamber, the walls may be formed of a substantiallyhomogeneous material (disposable plastics, glass, stainless steel, etc.)having substantially the same relative thickness. A description of anembodiment wherein a flexible plastic bag is provided with a cavity isdescribed below and shown in FIG. 22.

The pumping or mixing element 812 is capable of being positioned in thevessel 810 and includes a levitation magnet 816. In particular, thelevitation magnet 816 is sized and shaped for extending into theinterior of the annular portion 815 of the vessel 810. In theillustrated embodiment, the levitation magnet 816 is polarized in thevertical direction (the specific orientation of the poles is notcritical) to create a vertical magnetization vector. However, themagnetization vector could also be oriented in a horizontal orsubstantially horizontal plane (although those skilled in the art willrecognize that forming a single ring shaped magnet having opposite polesoriented in a horizontal plane is more difficult than forming one havinga vertical magnetization vector).

To levitate the pumping or mixing element in the vessel 810, at leastone, and preferably a plurality of superconducting elements 818 arepositioned in an annular cryostat 802. This cryostat 802 is speciallyadapted for receiving the annular protruding portion 815 of the vessel810 (see FIG. 19 a) and may even support the vessel, as shown in FIG.19. More specifically, in the illustrated embodiment. the cryostat 802includes an annular channel 806 for receiving the corresponding annularportion 815 of the vessel 810. The outer wall 808 of the cryostat 802defines a space or chamber that is preferably evacuated to create avacuum jacket, as described above. Alternatively, the chamber could befilled with an insulating material to reduce the thermal transfer.Regardless of the means used, the important point is that in the case ofpumping or mixing non-cryogenic, warm or temperature sensitive fluids,no or only negligible thermal transfer from the cold superconductor tothe vessel and hence the fluid results.

Preferably, the superconducting elements 818 are comprised of aplurality of segments, each of which is in thermal communication with acooling source (e.g., a Dewar flask or a closed-cycle refrigerator) viaa thermal link 820 positioned and supported in the cryostat 802. Thesegments comprising each of the one or more superconducting elements 818are preferably formed of a “high-temperature” superconducting materialhaving crystallographic A-B planes and a C-axis, which as noted above,is a characteristic of melt-textured or melt-processed ReBa₂Cu₃O_(x),with Re representing a rare earth element (e.g., Yttrium, of which YBCOis a common example).

In the preferred embodiment., three superconducting elements 818 a, 818b, 818 c are provided on the thermal link 820, although it should beappreciated from reviewing the description that follows that using onlya single superconducting element or two superconducting elements tolevitate the pumping or mixing, element 812 is entirely possible (seeFIG. 16). A first of the superconducting elements 818 a is positionedadjacent to a first side of the annular channel 806 formed in thecryostat 802 adjacent to a first side of the annular levitation magnet816. The second superconducting element 818 b is also positionedadjacent to a second side of the annular levitation magnet 816. Thethird superconducting element 818 c is positioned adjacent to a thirdside of the annular levitation magnet 816. Each of the superconductingelements 818 a, 818 b, 818 c may be in thermal communication with thesame thermal link 820, as shown in FIG. 19 and positioned internal tothe corresponding cryostat 802, which by way of insulation or vacuumjacket prevents any thermal transfer to the room temperature vessel 810,the fluid F held therein, or the pumping or mixing element 812.

In a most preferred version of this embodiment, the crystallographicplanes/axes of the segments forming the superconducting elements 818 a,818 b, 818 c are oriented so as to significantly improve the levitationforce, the resulting loading capacity, and the magnetic stiffness of thecoupling formed with the pumping or mixing element 812. Specifically,the first and third superconducting elements 818 a, 818 c (or moreparticularly, the segments comprising these elements) are oriented suchthat the C-axes thereof are perpendicular to the magnetization vector ofthe levitation magnet 816, while the second superconducting element 818b is oriented such that the C-axis of each segment thereof is alignedwith and parallel to the magnetization vector of the levitation magnet816. Another way to describe the arrangement is that the A-Bcrystallographic planes of the first and third superconducting elements818 a, 818 c are parallel to the axis of polarization of the levitationmagnet 816, while the A-B crystallographic planes of the secondsuperconducting element 818 b are perpendicular to the polarization axis(note the substantially parallel lines representing the A-B planes drawnon each superconducting element 818 a-c in FIG. 19). As used herein. theterms “parallel” and “perpendicular” are intended to mean generally orsubstantially parallel or perpendicular, it being recognized thatvariations in the orientation of the various crystallographic planes oraxes relative to the magnetization vector are either inherent or may becreated by slight misalignments of adjacent elements, or may beintentionally varied within a range to adjust or fine tune thelevitation force provided or rotational stability.

The particular arrangement shown in FIG. 19 results in a system 800 inwhich the pumping or mixing element 812 is levitated in a most stablefashion. This stable levitation results primarily form the interactionbetween the specially oriented segments forming each superconductingelement 818 a-c and the annular levitation magnet 816. As a result ofthis arrangement, the loading capacity of the pumping or mixing elementis increased, as it the stiffness of the magnetic coupling. Thiscombination allows for a greater amount of torque to be supplied to thepumping or mixing element 812 without accidental decoupling, whichallows for higher angular velocities to be achieved. It also allows foruse of the system 800 with fluids having higher viscosities.

The drive system for rotating the pumping or mixing element may besubstantially as described above. Specifically, a shaft 822 coupled atone end with a motive device, such as a motor 824, is positioned in aroom temperature bore or through an opening formed in the cryostat 802.The end of the shaft 822 adjacent to the vessel 810 carries a pluralityof drive magnets 824 having alternating polarities. Corresponding drivenmagnets 826 having alternating polarities are provided on the pumping ormixing element 812. As shown in FIG. 19, the pumping or mixing elementmay also include impeller blades 828, vanes, or like structures tofurther enhance the pumping or mixing action provided.

In accordance with yet another embodiment of the present invention, aspecific pumping or mixing system 900 using a rotating superconductingelement 901 is shown in FIG. 20. The superconducting element 901 may besupported by a plate 902 in thermal engagement with a cooling sourceforming a part of a cryostat 903 and preferably rotating therewith. Thesuperconducting element 901 is surrounded by a wall 905 defining anevacuated chamber 906, which may together be considered to form a vacuumjacket comprising part of the cryostat 903 (although as described abovethe chamber 906 could also be insulated or any other known or yet-to-bediscovered means for obviating thermal transfer between a coldsuperconducting element could be used).

In the illustrated embodiment, the cooling source is a portablerefrigerator or “cryocoole” 904 that also forms part of the cryoostat903. The cryocooler 904 is shown as having a “head” end 905 that extendsinto the chamber 906 to directly engage and support the plate 907 whichin turn supports the superconducting element 901, although the use of aseparate thermal link (not shown) is also possible, depending on therelative dimensions of the system. As with the thermal link previouslydescribed, both the plate 902 and the head end 907 of the cryocooler aretypically formed of a material having a high degree of thermalconductivity/low thermal resistance (e.g., a metal) to ensure that thedesirable efficient thermal transfer is established. The plate 902 mayalso be supported from the wall 905 by one or more connecting members908, which are preferably thin, but relatively strong, and formed of amaterial having a low degree of thermal conductivity so as to createonly negligible thermal transfer to the wall 905.

The cryostat 903 is rotatably supported by at least one, and preferablya pair of bearings or bearing assemblies 909 a, 909 b, which are in turnsupported by a stable support structure, such as an adjacent verticalwall VW or another type of support frame (which may or may not engagethe adjacent structure, such as table T, supporting the vessel). Forexample, one bearing may engage the outer wall 905 of the cryostat 903,while the other engages the outer wall of the cryocooler 904. The use oftwo bearing assemblies 909 a, 909 b of course ensures that the cryostat903 rotates about a vertical center axis in a most stable and reliablefashion and is capable of resisting any skewing forces, and may alsoallow it to be turned on its side (such as it would appear if FIG. 20 isoriented in a landscape view. rather than a portrait view). As shown inFIG. 20, the bearing assemblies 909 a, 909 b may include mechanicalroller or ball bearings, or other elements that may providelow-function, rotatable support the cryostat 903.

To transmit the desired rotational motion, an endless belt 910 may beplaced in frictional engagement with a first pulley 911 coupled to orcarried by the cryostat 903. The belt 910 also engages a second pulley912 supported by the shaft 914 of a motive device 916, such as avariable speed electric motor. As should be appreciated, the rotation ofthe shaft 914 thus causes the cryostat 903, and hence, thesuperconducting element 901 positioned therein to rotate. As notedabove, the cryostat 903 could also be mounted “inline” on a shaft thatis in turn connected or coupled directly to a motive device, such as anelectric motor.

One particularly preferred example of a commercially availableclosed-cycle refrigerator or cryocooler 904 for use in the presentinvention is a the of substantially self-contained, compact,closed-cycle cryocooler employing the Stirling cycle to produce thedesired refrigeration, several models of which are manufactured anddistributed by Suripower, Inc. of Athens, Ohio. As shown schematicallyin FIG. 20, this cryocooler 904 includes a lower portion 904 a whichserves to house an electric motor and an upper portion 904 b adjacent tothe head 907 which houses a reciprocating piston (not shown). In lightof the commercial availability of several suitable models. the workingsof such a cryocooler need not be understood to practice the presentinvention. However, it is noted that Sunpower, Inc. holds a number ofU.S. patents on various types of cryocoolers, each of which isincorporated herein by reference to the extent deemed necessary to allowa skilled artisan to make or use this invention. Regardless of the typeof cooling source used, the important point is that it is fully capableof generating the “high temperatures” (e.g. 77K-90K) necessary to inducea superconducting state in, for example, a YBCO superconducting element(which may be comprised of a plurality of segments, as described below).

To supply the necessary power to the cryocooler 904 such that it keepsthe superconducting element 901 at the desired temperature, yet allowsit to rotate even at high speeds, a dynamic electrical connection isprovided. Specifically, contacts 918, which are shown in the form ofannular rings surrounding the outer wall of the cryocooler 904, areprovided for engaging corresponding “stationary” flexible or pivotingcontacts 920 in electrical communication with a power source 922(120/220V), which may be remote. As should be appreciated, thisconfiguration allows the cryocooler 904 to freely rotate at both highand low speeds while continuously receiving the power necessary to runthe motor/drive the piston and keep the head end 907 at the desired coldtemperature. Instead of this illustrated configuration, a well-knowntype of dynamic electrical connection called a “slip ring” may be used,such as those manufactured by Siemens, Litton, and the Kaydon Corp. Aslip ring is also sometimes referred to in the art as a “rotaryelectrical interface,” a “commutator.” a “swivel,” or a “rotary joint.”

The system described above can be substituted into the system 100 shownin FIGS. 5-7 for rotating a pumping or mixing element in the form of aflat, disc-shaped rotor or impeller 134 for pumping or mixing a fluid ina flat-bottomed rigid vessel or bag. In that case. the plate 902 couldbe eliminated and a disc-shaped superconducting element, such as element106, used in its place. However, in FIG. 20, the vessel 922 isillustrated having a cavity 924, which may of course be similar inconstruction to the cavity provided in a vessel capable of withstandinghigh internal pressures, as described above and shown in FIG. 16.Alternatively, the cavity 924 could be formed in a conventional open-topvessel, in a flexible bag or container (see FIG. 22), or in any othertype of vessel used in applications where high pressures are not aconcern. In the case where the cavity 924 is formed in a flexible bag orcontainer, as shown in FIG. 22, is should also be appreciated that thecavity 924 may serve a function similar to that of centering post 528shown in FIG. 14 b (and could even include a peripheral flange,projections, or like structures at the upper end to ensure that thepumping, or mixing element 926 remains fully held in place duringshipping, storage, or between uses, yet spaced far enough away to avoidcreating any interference with the desired levitation/rotation).

In any case, in the embodiment in FIG. 20, the pumping or mixing element926 is substantially cylindrical and includes only a levitation magnet928, since both the levitation force and the driving torque are providedby the superconducting element 901. This levitation magnet 928 may becomprised of a plurality of segments of permanent magnets 928 a . . .928 n having alternating polarities and arranged in a substantiallyannular or polygonal configuration (see the schematic illustrationmerely showing a preferred orientation/arrangement in FIG. 21). As alsoshown schematically in FIG. 21. the superconducting element 901 isconcentric with the levitation magnet 928 and is also comprised of aplurality of segments 901 a . . . 901D arranged in an annular orpolygonal configuration. Preferably, each segment 901 a . . . 901 n isoriented having its crystallographic C-axis aligned in the radialdirection (i.e., oriented generally parallel to the magnetization vectorof a corresponding segment 928 a . . . 928 n of the permanent magnet928, and preferably passing substantially through the center thereof).Accordingly, the A-B planes of the segments 901 a . . . 901 n comprisingthe superconducting element 901 are oriented generally perpendicular tothe radial direction. and hence, the magnetization vector. As a resultof this arrangement, the rotating superconducting element 901 not onlyreliably induces stable levitation in the pumping or mixing element 926via levitation magnet 928, but also forms a magnetic coupling whichcauses the pumping or mixing element 926 to rotate. As shown in FIG. 20,the pumping or mixing element 926 may also carry one or more impellerblades, vanes, wings, or like structures 930 to further enhance thepumping or mixing action.

FIG. 23 shows an embodiment of the pumping or mixing system 950 for usewith a vessel (such as a tank K, but any vessel disclosed herein wouldalso work) having a cavity that is generally similar to the embodimentshown in FIG. 20 with a few modifications. The first is that therotating cryostat 952 includes two arrays of superconducting elements954, 956, with each array spaced in the vertical direction. The pumpingor mixing element 958 includes corresponding arrays of alternatingpolarity magnets 960, 962 (see, e.g., FIG. 21), with each magnet in thearray 960 having a neighboring magnet with an alternating polarity. Therotation of the cryostat 952 and, hence, the superconducting elementarrays 954, 956 thus induces both levitation and rotation in the pumpingor mixing element 958 (which is shown having a plurality of upstandingblades B). As should be appreciated, the dual arrays enhance thevertical stiffness of the coupling and improve torque transfer.

The superconducting element arrays 954, 956 are supported on a thermallyconductive platform 963 by an upstanding cylindrical wall 964. Theplatform 963 in turn is coupled to a rod 965 serving as a thermal linkto a cooling source, such as the SUNPOWER cryocooler described above ora Dewar flask filled with a liquid cryogen, which is in turn coupled toa motive device (shown in block form only, but see FIG. 20 for anexample of one possible embodiment). As noted above, insulating orevacuating the chamber 966 in the cryostat 952 prevents the coldsuperconducting element arrays 954, 956 from cooling the adjacent tank Kto any significant degree, which means that the system is well-adaptedfor pumping or mixing non-cryogenic fluids, including room-temperaturefluids.

The embodiment of FIG. 23 also differs from the one shown in FIG. 20 inthat the pumping or mixing element 958 carries a first ring magnet 968(or an equivalent array of magnets, such as vertically polarizedmagnetic discs (not shown)). A corresponding ring, magnet 970 (or arrayof magnets) is carried by the rotating cryostat 952 (preferablyexternally and at the top, as shown in FIG. 23). The first ring magnet968 and the second ring magnet 970 are oriented such that like poles areadjacent to each other. This magnet-magnet interaction thus repels thepumping or mixing element 958 from the cryostat 952. However, theinteraction between the superconducting element arrays 954, 956 and thearrays of magnets 960, 962 together generally levitate and hold thepumping or mixing element 958 in place. The net result is that thepumping or mixing element 958 is levitated, but is able to resist anyforce tending to move it into contact with the tank K, including theouter surface of the adjacent cavity.

Another distinction in the illustrated embodiment is that the pumping ormixing element 958 is generally cylindrical and includes an opening 967.As a result of this construction, when the pumping or mixing element 958is rotated, fluid is drawn into the gap between it and the adjacentcavity in the tank K (see action arrows F). The fluid then passesthrough the opening 967, which enhances the fluid agitation created bythe rotation of the pumping or mixing element 958, even at relativelylow angular velocities.

A related embodiment is shown in FIG. 24. In this embodiment, the firstring magnet 968 (or array) is again provided on or in the pumping ormixing element 958, but the second ring magnet 970 (or array) ispositioned external to the tank K. Again, the rings 968, 970 have likepolarities along the adjacent faces to create a repelling force. In thiscase, this force helps to prevent the pumping or mixing element 958 from“bottoming out” on the adjacent surface of the tank K. Although notpreferred for most applications due to the clean-up and sterilizationproblems possibly created, the second ring magnet 970 could bepositioned just inside the tank K as well. Instead of attaching the ringmagnet 970 to the tank K, it could also be supported by the cryostat952, such as a flange (note dashed lines in FIG. 24) or a relatedstructure that rotates therewith. Also, the possibility of providingneighboring magnets in each array 960, 962 with like polarities is shown(with the polarities of vertically adjacent magnets in each array stillalternating), which is somewhat less preferred than the embodiment ofFIG. 23 in which the polarities of neighboring magnets in each arrayalternate.

These two approaches could also be combined into the same system, asshown in FIG. 25. In particular, first and second ring magnets 968 a,970 a are provided in one portion of the pumping or mixing element 958,and third and fourth ring magnets 968 b, 970 b are provided in another.The repelling forces created thus provide dual levels of protectionagainst the rotating pumping or mixing element 958 inadvertentlycontacting the vessel or tank K. Also, either or both approaches couldbe used in the embodiments of FIG. 16 or 19 as well. Also note that thepolarities of adjacent magnets in the arrays 960, 962 are alike,although each vertically adjacent pair has a different polarity that thenext-adjacent pair. This is somewhat less preferred than the arrangementof FIG. 23 in terms of stiffness, but would work nevertheless.

By switching the polarities, it is also possible to provide one or moresets of magnets like ring magnets 968, 970 that attract, rather thanrepel each other. The attractive force thus created may help to preventthe pumping or mixing element 958 from moving in a vertical directionrelative to the cavity as it rotates (or in the horizontal direction, inthe case where the cavity is positioned with its centerline axisparallel to a horizontal plane). The magnets would preferably besufficiently weak in power to avoid creating any instability in thelevitation and/or rotation induced by the superconducting element arrays954, 956.

FIGS. 26 and 27 show a method and apparatus for centering and setting upa pumping or mixing element 980 that is capable of levitating in avessel 981, such as in a hermetically sealed tank in a sterile vessel,such as a flexible bag, or even in an open-top vessel where access tothe corresponding surface adjacent to levitating the pumping or mixingelement is restricted. The vessel 981 includes a cavity 982, asdescribed above. Inside the vessel 981, the cavity 982 may include alongits outer surface an engagement structure for contacting, engaging, orsupporting the pumping or mixing element 980 when in a non-levitating orresting position. In the preferred embodiment, this engagement structurecomprises a frusto-conical surface 984 that is tapered relative to thehorizontal plane. The pumping or mixing element 980, which is of coursegenerally annular, includes a matching surface 986 along at least aportion of an adjacent inner surface thereof.

Preferably, the matching surface 986 is formed in an inert portion ofthe pumping or mixing element 980. such as the matrix material (e.g.plastic, metal, composites, etc.) used to support the levitation magnetor magnet array 988 (which is shown schematically, but could be anyappropriate one of the arrangements described herein). The pumping ormixing element 980 is shown slightly raised in the vertical direction toillustrate the shape of the surfaces 984, 986. However, it should beappreciated that these surfaces 984, 986 would normally be in contactwith each other as the result of gravity when the pumping or mixingelement 980 is at rest (i.e., non-levitating), such that a radialcentering function is inherently provided.

A cryostat 989, which may be substantially identical to those describedabove, is positioned in the cavity 982. In particular, the cryostat 989contains one or more superconducting elements 990 (which may in turn beformed of segments) that are mounted on a platform 983 that is in turncoupled via thermal link 991 to a cooling source, which in view of thevarious versions described herein is merely shown in block form. Theentire cryostat 989 is preferably coupled to a second motive device 994,also shown in block form, that rotates it along with the superconductingelement(s) 990. It may also be coupled to a second motive device formoving it relative to an inner surface of the cavity 982, such as in thevertical direction as shown in FIG. 26. As described above, in the caseof non-cryogenic fluids, the cryostat 989, or at least the portionhousing the superconducting element(s) 990 and any other cryogenicstructures, is preferably evacuated or insulated to prevent thermaltransfer to the adjacent vessel 981.

To form a magnetic coupling between the superconducting element(s) 990and the levitation magnet 988 of the pumping or mixing element 980, thecryostat 989 is moved to a position within the cavity 982 where thesetwo structures are substantially aligned. In particular, the alignmentis such that the superconducting element(s) 990 face the adjacentlevitation/driven magnet(s) on the pumping or mixing element 980, whichof course is inside of the vessel 981. Once this alignment is achieved,the superconducting element(s) 990 are cooled to below the transitiontemperature (preferably less than 90K for a YBCO superconductor) inaccordance with a field cooling protocol. As a result, a magneticcoupling is established with the levitation/driven magnet 988 and thedesired pinning forces are created that permit stable, exceptionallyreliable levitation of the pumping or mixing element 980 (and rotation.in the case where the superconducting element 990 is rotated, such as byusing the configuration shown in FIG. 21).

Once the magnetic coupling is formed, the cryostat 989 may be movedfurther into the cavity 982, either manually or rising a third motivedevice 996, such as a linear actuator or the like. As a result of thecoupling formed between the superconducting element(s) 990 and thelevitation magnet 988, this causes the matching surface 986 of thepumping or mixing element 980 to separate from the frusto-conicalengagement surface 984 (see FIG. 27 and note action arrow Z). Rotationof the cryostat 989 using the second motive device 994 may then beeffected as described above to cause the levitating pumping or mixingelement 980 to rotate and, hence, pump or mix the fluid in the vessel981.

To return the pumping or mixing element 980 to a resting position suchthat contact is re-established between surfaces 984, 986, thesuperconducting clement(s) 990 need only be returned to above thetransition temperature, at which point the magnetic coupling is lost. Toexpedite this operation, and as described above, a heater 998 may beused. Once the coupling is no longer formed, it should be appreciatedthat the pumping or mixing element 980 gently comes to rest such thatthe surfaces 984, 986 are in engagement and the desired centeringfunction is provided as a result of the matching tapers or slopes.Advantageously, this means that the user of the system need not haveaccess to the pumping or mixing clement 980 to ensure that it isproperly centered for purposes of field cooling prior to levitation, andactually avoids the need for the use of a set-up kit, as described above(which in this case could be hat-shaped with a set-up or charging magnetcorresponding in magnetic field and polarity to levitation magnet beingplaced over the head end of the cryostat 989).

The use of this “moving cryostat” arrangement with the other embodimentsof pumping or mixing systems disclosed herein is also possible, and inparticular, with the embodiment shown in FIGS. 19, 20, 23-25 (which mayrequire adjusting the relative dimensions or adding an annular piece ofinert material to the pumping or mixing element to provide the matchingsurface 986). Also, instead of forming the frusto-conical surface aspart of the cavity 982, it could actually be a separate, freestandingstructure positioned at the same location or adjacent to the outersurface of the pumping or mixing element 980 (see the phantom depictionof engagement structure 999 in FIG. 27), in which case the matchingsurface 986 would be positioned accordingly (i.e., along the outersurface of the pumping or mixing element 980). The entire arrangementcould also be inverted (not shown), with the engagement surface 984being provided on the upper end of the cavity 982 and the matchingsurface 986 being on a corresponding surface of the pumping or mixingelement 980 (in which case, the cryostat 989 would be withdrawn from thecavity 982 once the desired magnetic coupling is formed). If the vessel981 is inverted, the cavity 982 would preferably be elongated to avoidinterfering with the adjacent wall of the vessel 981.

Each of the embodiments of pumping or mixing systems disclosed herein10, 100, 200, 300, 700, 800, or 900 could also be used for mixing afluid with a product, such as a bacterial nutrient culture media,eukaryotic cell nutrient culture media, buffer, reagent, or likeintermediate product for forming one or more end products. As a resultof the levitating nature of the pumping or mixing element, applicationof these systems to vessels where the product and the pumping or mixingelement are sealed in the vessel before use, including in an asepticenvironment, is of course possible.

In summary, a number of systems 10, 100, 200, 300, 700, 800, 900 as wellas variations on these systems and related methods, are disclosed thatuse or facilitate the use of superconducting technology to levitate amagnetic element that, when rotated, serves to pump or mix a fluid. Inone system 10, the magnetic element 14 is placed in a fluid vessel 16positioned external to a cryostat 12 having an outer wall or otherhousing 18 for containing a superconducting element 20. A separatecooling source 24 (either a cryogenic chamber 26, FIGS. 1 and 3 or arefrigerator 48, FIG. 2) thermally linked to the superconducting element20 provides the necessary cooling to create the desired superconductiveeffects and induce levitation in the magnetic element 14. Since thepumping or mixing element levitates in the fluid F, no penetration ofthe vessel walls by mixing, or stirring rods is necessary, whicheliminates the need for dynamic bearings or seals.

Additionally, the outer wall 18 of the cryostat 12 or other housingdefines a chamber 25 that thermally isolates and separates thesuperconducting element 20 from the vessel 16 containing the fluid F andpumping or mixing element 14. The thermal isolation may be provided byevacuating the chamber 25, or filling it with an insulating material. Byvirtue of this thermal isolation and separation, the superconductingelement 20 can be positioned in close proximity to the outer wall orhousing 18 adjacent to the vessel 16 and pumping or mixing element 14,thereby achieving a significant reduction in the separation distance orgap G between the pumping or mixing element 14 and the superconductingelement 20. This enhances the magnetic stiffness and loading capacity ofthe magnetic levitating pumping or mixing element 14, thus making itsuitable for use with viscous fluids or relatively large volumes offluid.

The exceptionally stable levitation provided as a result of the reducedseparation distance also significantly reduces the potential for contactbetween the rotating pumping or mixing element and the bottom orsidewalls of the vessel. This makes this arrangement particularlywell-suited for use in fluids that are sensitive to shear stress or theeffects of functional heating. However, since the superconductingelement 20 is substantially thermally isolated and separated from thevessel 16, the magnetic element 14, and hence the fluid F containedtherein, may be shielded from the cold temperatures generated by thecooling source 24 to produce the desired superconductive effects and theresultant levitation. This allows for temperature sensitive fluids to bemixed or pumped. By using means external to the vessel 16 to rotateand/or stabilize the magnetic element 14 levitating in the fluid F, suchas one or more rotating driving magnets coupled to the magnetic element14, the desired pumping or mixing action is provided.

Additional embodiments of systems 100 (900), 200 for pumping or mixing afluid wherein the necessary motive force is provided from the same sideof the vessel at which the superconducting element is positioned arealso disclosed, as are systems 300, 400 for rotating an inline pumpingor mixing element positioned in a vessel in the form of a pipe or thelike in a similar fashion. Alternative systems 700, 800, and 900 arealso disclosed, which are particularly well adapted for applicationsusing special vessels having cavities that assist in withstanding highinternal pressures. Particular orientations of the crystallographicplanes of the material used as the superconductor are also described toenhance the levitation force and magnetic stiffness of the coupling,which in turn increases the stability and load capacity of the pumpingor mixing element, as is the use of opposing pairs of permanent magnetsto provided a levitation-assist function. A manner of centering andsetting up a pumping or mixing element in a hermetically sealed vesselis also disclosed.

The foregoing description of various embodiments of the presentinvention have been presented for purposes of illustration anddescription. The description is not intended to be exhaustive or tolimit the invention to the precise forms disclosed. Obviousmodifications or variations are possible in light of the aboveteachings. For example, while the use of a thermally separatedsuperconducting element is disclosed, the subsequent development of roomtemperature superconductors would obviate this need. Instead of using asuperconducting element as the motive device, another option is to use aseparate drive structure (e.g. an electromagnetic coil) to form acoupling capable of transmitting torque to the particularfluid-agitating element (which may be “levitated” by a hydrodynamicbearing; see, e.g., U.S. Pat. No. 5,141,327 to Shiobara). Theembodiments described provide the best illustration of the principles ofthe invention and its practical applications to thereby enable one ofordinary skill in the art to utilize the invention in variousembodiments and with various modifications as are suited to theparticular use contemplated. All such modifications and variations arewithin the scope of the invention as determined by the appended claimswhen interpreted in accordance with the breadth to which they arefairly, legally and equitably entitled.

1. An apparatus for mixing a fluid, comprising: a vessel including aflexible wall at least partially defining an interior compartmentcapable of receiving and holding the fluid; a fluid-agitating element inthe interior compartment of the vessel; and a receiver secured to theflexible wall of the vessel for receiving the fluid-agitating element.2. The apparatus of claim 1, wherein the fluid-agitating element isdisengaged from the receiver and capable of rotating relative to thereceiver and moving toward or away from the wall of the vessel.
 3. Theapparatus of claim 1, wherein the receiver includes a retainer forretaining the fluid-agitating element.
 4. The apparatus of claim 1,wherein the fluid-agitating element includes a passage for receiving thereceivers said passage including an opening at one end having atransverse dimension larger than a corresponding dimension of thereceiver.
 5. The apparatus of claim 1, wherein the receiver comprises animperforate sidewall forming a cavity.
 6. The apparatus of claim 1wherein the receiver includes an inner surface for contacting the fluidwhen present in the vessel and an outer surface external to the interiorcompartment for positioning adjacent a motive device for rotating thefluid-agitating element.
 7. The apparatus of claim 1, wherein thefluid-agitating element includes a home or resting position and iscapable of levitating relative to the receiver to an active position. 8.The apparatus of claim 1, further including a motive device for rotatingthe fluid-agitating element, the motive device including an upperportion matching a corresponding outer surface of the receiver.
 9. Theapparatus of claim 1, wherein the fluid-agitating element comprises asubstantially cylindrical body having an outer wall spaced from asidewall of the receiver.
 10. The apparatus of claim 1, wherein theflexible wall of the vessel includes an opening said receiver being atleast partially within the opening of the vessel.
 11. An apparatus formixing a fluid, comprising: a vessel including a flexible wall at leastpartially defining an interior compartment capable of receiving andholding the fluid; and a rotatable fluid-agitating element for agitatingthe fluid in the interior compartment of the vessel; the vessel furtherincluding a receiver having a projecting portion with a sidewall and anendwall defining a cavity, said projecting portion including an outersurface in communication with the environment exterior to the interiorcompartment of the vessel and an inner surface within the interiorcompartment of the vessel and adjacent the fluid-agitating element. 12.The apparatus of claim 11, wherein the fluid-agitating element ispositioned adjacent the inner surface of the cavity within the vesseland retained adjacent the receiver by a coupling.
 13. The apparatus ofclaim 11, further including a retainer for providing a retentionfunction to maintain the fluid-agitating element adjacent the innersurface of the cavity.
 14. The apparatus of claim 11, further includinga rotatable rod positioned in the cavity adjacent the outer surface,said rod adapted for being rotated by a motor for inducing rotation inthe fluid-agitating element.
 15. The apparatus of claim 11, furtherincluding a bearing for facilitating rotation of the rod relative to thevessel.
 16. The apparatus of claim 15, wherein the bearing is positionedbetween a motor for rotating the rod and the vessel.
 17. An apparatusfor mixing a fluid, comprising: an at least partially flexible vesselincluding an interior compartment; means for agitating the fluid whenpresent in the interior compartment; and means for receiving thefluid-agitating element.
 18. The apparatus of claim 17, wherein themeans for agitating comprises a rotatable, generally cylindricalfluid-agitating element for positioning in the interior compartment ofthe vessel in contact with the fluid when present.
 19. The apparatus ofclaim 17, wherein the means for receiving the fluid-agitating elementcomprises a post protecting within the interior compartment.
 20. Theapparatus of claim 17, wherein the means for receiving comprises aprojecting portion of the vessel, said projecting portion having asidewall and an end wall defining a cavity, said projecting portionfurther including an outer surface in communication with the environmentexterior to the interior compartment of the vessel and an inner surfacewithin the vessel for contacting the fluid when present and adjacent thefluid-agitating element